Hmmmm interesting concept .... using G-Sync over 100 fps ... why would anyone do that ? Kind alike saying.... "On our trip to disneyland, I took my Jeep rental from Orlando to "The Keys" and on the way back I locked the hubs and drive back in 4WD an I noticed mileage drops .... WTH ?
Yeah, WTH .... what they hell would you drive in 4WD on a Florida Highway ?
G-Sync works from 30 fps and has its most significant impact from 30 - 70 fps since it trails off after 60. Freesync works the same way (40 - 70 fps) as again the impact trails off once ya get above 60. Where they differ is that, once you can maintain > 60 fps, you turn G-Sync off and switch to ULMB.
Let's make it simple ....
NVidia G-Sync Monitor
30 - 60 / 70 fps - Use G-Sync
60 / 70 fps on up - Use ULMB
AMD Freesyn Monitor
30 - 60 / 70 fps - Use FreeSync
60 / 70 fps on up - No alternatives unless Monitor Manufacturer provided one
My son has SLI on his 1440p and rarely turns off G-Sync since he's above 80 fps most of the time.
G-Sync monitors do incude a cost premium to cover the cost of the strobing module which provides ULMB. AMD, as has been their modus operandi, chose to compete on price and that strategy has served them well. Some Monitor vendors have filled that void by offering their own strobing / blur reduction alternative to fill that gap..
Asus ROG XG27VQ - ASUS ELMB
BenQ XL2730Z - BENQ Blur Reduction
EIZO Foris FS2735 - EIZO Blur Reduction
LG 24GM79B - G Blur Reduction
LG 34UC79G - LG Blur Reduction
Samsung C49HG90 - Samsung
Samsung C24FG70 - Samsung
Samsung C27FG70 - Samsung
But yes no doubt as cards get more powerful, 144 Hz 4k becomes affordable, and games add more load, we are going to see games that get weird in SLI in 40 - 60 fps zone.... I been saying fo 3 generations now that nVidia is nerfing SLI because there is no competition on the top tiers so SLI was hurting the sale of their top tier cards. Can find no other explanation why across the test suite, scaling is 18% at 1080p, 33% at 1440p and amazingly, 54% at 2160p. While it has a very narrow range of impact, hopefully if SLI has been intentionally nerfed, this will force nVidia to address it.