Sounds like you are not using a vertical total tweak!
(DVI connections require the ToastyX pixel clock patcher for VT tweaks, Displayport does not).
Even the Gsync monitors and the Benq XL2730Z 1440p blur reduction monitor will have the exact same issues you are experiencing.
This happens because on TN and IPS panels, the pixels themselves have a transition time that is needed to complete a color transition change when a pixel changes colors. Depending on the color origin and target change, this can be anywhere between 5 ms to 18 ms.
The average time for pixel transitions is usually around 8 ms. Keep in mind that this is different from refresh rate input lag, which is lowest at the top of the screen (can be as low as 2ms) and highest at the bottom of the screen (~18ms).
If blur reduction is off, input lag doesn't affect image quality at all, just response time. Pixel transition time causes blurriness and streaking. There will always be blurriness, but if a panel had a 0ms pixel response time (think OLED here), you would have absolutely NO streaking and no artifacts at all, just blurriness based on the refresh rate itself. But this is impossible with LCD panels.
With TN/IPS, etc, overdrive settings help try to reduce the streaking and extra blurriness due to slow pixel transition times, by increasing voltage to speed things up, but on many color transitions, since the voltages for "Short" transitions will be DIFFERENT than long transitions, the short transitions will get "overshot" (too much voltage), causing an unwanted swing in the opposite direction. This is what you call "overdrive artifacts" and the effect is, you get "Inverse" copies of the primary image. Also known as inverse ghosting or RTA artifacts.
Blur reduction seems to highlight both overdrive artifacts (due to the removal of motion blur) **AND** unlike non blur reduction, it *ALSO* highlights artifacts caused by PIXELTRANSITION TIMES (e.g. input lag). This is hard to explain easily, but basically, think of this.
Let's say you are at 120hz refresh rate, ok?
120hz refresh rate "input lag" or better called "FRAME LAG" is equal to 1000 / refresh rate or 1000 divided by 120 here for this example.
This is equal to 8.3, with the answer in milliseconds. For 60hz its 1000 /60=16.7ms, for 100hz its 10ms, for 144hz its 1000/144=6.9ms.
This is easy to follow, right?
now remember what I told you about pixel response times?
Pixel response times DO NOT CHANGE WITH REFRESH RATE and are UNAFFECTED by refresh rate! They are based on the physical panel characteristics! Even increasing overdrive settings does not change the *RAW* pixel response times! It just affects certain color shades but you can't turn metal into lemonade, you know!
So lets think about how this affects things. it's actually blatantly obvious.
Remember what I told you about input lag? based on refresh rate?
Top of screen: 2ms.
Middle of screen: 7ms.
bottom of screen: 18ms.
Now...what is the raw FRAME TIME of 120hz?
Do you remember it?
Do you see the problem ?
Once you get past the "middle" of the screen, the "frame lag" time gets BELOW the refresh rate input lag time, with the screen updating to to bottom. So what happens?
The NEXT frame after the current frame starts being displayed on the screen at the same time as the current frame!
Due to blur reduction removing "persistence" blurring, you start seeing screen data from the next frame as you move down the screen, begin to "mix" with screen data from the current frame. this is called "Strobe crosstalk."
if blur reduction is off, you don't see any of this, because the entire screen is always visible at once, so the only thing you would notice would be an increase in input lag from the top to the bottom of the screen. You wouldn't see a change in colors or frame data, and you would need equipment to measure the input lag difference.
The "Area" or "Strobe Phase" setting changes at what "time" during a screen refresh period the strobing begins and ends. that's why it's called strobe phase. Strobe phase of "000" is the latest strobe phase--you begin the strobe at the END of the current frame (meaning you actually have one frame of HIGHER INPUT LAG total), because the information on the screen is the NEXT frame, not the current frame.
Strobe phase of "100" is the EARLIEST strobe phase. Here you start the strobe during the CURRENT frame. But strobe phase of 100 will cause more crosstalk on the screen, at the bottom. The bottom will be the next frame appearing on top of the current.
Lightboost monitors do this already, but for Benq blur reduction, you can use something called a "Vertical Total" tweak, to INCREASE the amount of blanking time during a frame, which gives the screen pixels more time to finish their color transitions before the next frame's data can overwrite and mix up with it. This does cause an "increase" in input lag, but only on the order of a MAXIMUM of 0.167ms per strobe persistence point, with the real input lag completely unmeasurable. By using a Vertical Total tweak, you will be helping lower the amount of strobe crosstalk at the bottom of the screen by a large margin.
note: VT tweaks do NOT work on the XL2730Z.
Please note: the maximum "Strobe Phase" (Service menu on XL 2430T/2720Z/2411Z/2420Z), also called "Area" on the XL2430T, will be LIMITED if you use a VT tweak. For 120hz, the maximum strobe phase will be cut in half, from 100 to 50, because 120hz is double 60hz.
Maybe that "120hz being double 60hz" might not make sense to you, but all the math and explanations are given here:viewtopic.php?f=13&t=2590
you may not understand this right away, but take your time and do the math. Eventually it will make a lot of sense to you.
tl;dr: Use VT 1500 for 120hz.
if using DISPLAYPORT instead of DVI, use Horizontal total 2001 and VT 1499 at 120hz, to keep BPC at 8 bpc instead of reverting to 6bpc. Displayport 1.1a limitations limit 8bpc to 359.99 MHz pixel clock.
use VT 1502 for 100hz. (VT 1502 at 120hz is randomly unstable when set and can frameskip).
I'll summarize two things which explain why the maximum strobe phase gets limited:
1) For reasons unknown, using ANY vertical total tweak changes the STROBE BASE PERSISTENCE to the 60hz values (0.167ms).
Usually, base strobe persistence is simply equal to Refresh rate persistence/100 or Refresh persistence divided by 100.
Refresh rate persistence is equal to 1000 divided by refresh rate.
Example: 120hz: base persistence =6.9ms
base strobe persistence =6.9ms / 1000 = 0.069 ms.
VT tweak FORCES base strobe persistence to 60hz values: 16.7ms / 100 = 0.167 at ALL REFRESH RATES!!!!!!
2) Maximum strobe phase value = Refresh rate persistence / base strobe persistence. (remember: VT tweak forces BASE STROBE PERSISTENCE to 0.167).
(example: 100hz: 10ms divided by 0.167 = 59.88 max strobe phase).