I have a BENQ XL2730Z with Freesync. I play only CSGO, so for a strenuous test of the monitor, this is probably not the right game. My PC is a 5930X Intel, MSI X99S MPOWER, 32GB RAM, SSD/HDD, AX860i. I was using a Sapphire Radeon R9 295x2 and getting 290-299FPS, but substituting an MSI R9 290 Gaming (4GB) also gets around 290-299 FPS at peak. The game average FPS is all over the map due to something in Catalyst, I am sure. Once I replaced the DVI-D connection with a DP1.2 cable connection, both cards cause Catalyst to ask if I want to activate Freesync. Once I do, the FPS drops down a bit but lows are no longer in the 30s and 40s, but in the 80s and 90s, and highs rarely get above 200 FPS. BUT....the game is WAY smoother, and actually looks MUCH better due to the sync. I run the monitor at 144Hz, so I am asking the best from it, but the sync seems to make quite the difference. Since the R9 290 seems to do as well as the 295x2, I am now using only that card for CSGO since the 295x2 is overkill and quite the power hog. I am building a second gamer, and it will have GTX980Ti cards in SLI, and I fully expect to try the ASUS ROG G-sync 1440p monitor on that.
Prior to this I was gaming on XFX 7970s in Crossfire using a Samsung 305T, 2560x1600. although that also provides massive FPS in CSGO is also has a bit of tearing. The Samsung does not have the same response time either, and its scan in fixed. I can say that the use of a sync-related solution seems to truly increase my enjoyment of the game, but its a pretty penny to get there. But gaming now at 1440p or higher is very spoiling, and I have a hard time using a FULL HD screen. Oops.
By the way, even when not gaming, and doing other work on the PC, the BENQ XL2730Z is amazing. Such a great display, and so well packaged. I am entertaining another one for my wife's work PC at home. Its really bright, and helps her focus.