Short answer:
You should be good. XG270 has similar overdrive in FreeSync ON versus FreeSync OFF for max-Hz (240Hz) so the look is fine.
Long Answer:
First, just to be clear, "GSYNC lag" is confusing, because:
1. GSYNC/FreeSync is generally the world's lowest lag "non-VSYNC-OFF" sync technology.
2. "GSYNC lag" comes mainly from framerates trying to exceed refresh rates, as well as the lag inconsistency at the crossing threshold (fps < Hz) versus (fps >= Hz)
3. Some monitors have different processing latencies for VRR ON/OFF but sometimes they're quite similar, if you meet certain conditions
(The esports community parrots about GSYNC lag, without fully understanding what "GSYNC lag" is, and how to avoid it)
More information can be found in GSYNC 101 on this,
www.blurbusters.com/gsync/gsync101
Now, that being said,
most of the time (if the monitor is designed correctly), enabling GSYNC/FreeSync monitor side but disabling on driver side, will have similar lag to having both sides turned off. So you should be OK. However, some changes may occur such as the inability to turn on PureXP or other tweaks (e.g. unable to adjust overdrive). Which may affect GtG pixel response time and affect/improve/equalize lag indirectly (but this is not VRR lag).
For those who wishes to play GSYNC in esports, I always recommend the fastest scanout available (to avoid scanout lag,
www.blurbusters.com/scanout ... as well) as a VRR range wider than frame rate range, so capping becomes unnecessary. Unfortunately, that is difficult to do without a 360 Hz GSYNC monitor though (where it's easy to fit 100fps-300fps completely within the VRR range of a 360 Hz monitor). That's the best way to avoid "GSYNC lag" -- ultrafast scanout + humongous VRR range beyond framerate range.
That said, if you just want to play VSYNC OFF, it is usually acceptable to leave VRR enabled monitor-side, unless its processing is extremely laggy. Try it both ways to verify -- and check the most reputable sources -- it varies from monitor to monitor.