I wasn't aware that ULMB can do 60Hz single-strobe on many monitors that don't actually support it officially. Mine only goes down to 85Hz by default. I've seen people here report that VT tweaks can force 60Hz ULMB, so I tried that and it worked just fine on my monitor (a ViewSonic XG2703-GS.)
If you want to try it, here's how to do it:
In CRU, find the lowest mode that can do ULMB. Also look in the extension block if the mode doesn't appear on the main list. Here, it's the 2560x1440@85Hz mode. Double-click the mode. Make a note of the pixel clock value (here it's 346.50MHz.) Click the "Copy" button. Cancel the dialog.
Open the 60Hz mode (double-click it.) Make sure you're editing the native 60Hz mode, not some low-resolution one. Leave the "Timings" drop-down list at "Manual"; don't change it. Click the "Paste" button. In the refresh rate box, enter "60.007" (more on that later*.) Click the "Total" radio button, and in the "Vertical" box enter a value high enough so that the pixel clock becomes equal to the value you noted before (346.50MHz in my case.) If you can't get it exactly right, get it as close as possible. In my case, that's 2123, and the final pixel clock value is 346.52MHz.
And that's it. Confirm all dialogs until CRU closes, and run the "restart64.exe" program (or "restart.exe" on 32-bit). Make sure G-Sync is disabled in the nvidia panel, then switch to 60Hz, and in the monitor's OSD try to enable ULMB. If it works, congratulations If not, you can try and play some more with the timings (for example by copying timings from other ULMB-modes instead of the lowest ULMB-capable mode). Could be hit-and-miss. If nothing works, you can revert all the changes you did in CRU by running "reset-all.exe" and rebooting.
Beware though: If ULMB works, the flicker is more severe than 85Hz ULMB, and MUCH more severe than 100Hz ULMB. I'm not a doctor, but you might not want to try this if you're prone to seizures
*As for the "60.007Hz" value we entered above, that's just a trick to get lower input lag with vsync by using RTSS to cap to 60FPS. 60.007Hz with a 60FPS cap will lower input lag without introducing noticeable micro-stutter.