It should not cause a problem but i would upgrade to a r9 290 or 290x when aftermarket cards come out since Mantle will be a larger change to gaming than gsync.
Lower level control is nice but gpu controlled scan is completely new. Fixed scan frequency should be abandoned since we are supporting it only because it's a CRT/TV legacy. A gpu controlled scan doesn't even require that much processing power since it "theoretically" never miss a scan and gives you minimum input latency.
The R9 290 is in my budget range, yet I really can't make my mind over it as the reference cooler did a mess and worst than ever AMD distributed good GPUs to reviewers and the retail ones are completely different.
I got time to figure all this out since I won't start buying until the monitor comes out. Anyway I'm in for a 144Hz monitor. I played on the VG248QE last month in a PC store, and loved it. High resolutions, 4K and triple monitor (with idiot bezels)? No, thanks. I liked the responsiveness a lot and the chance to miss a scan are halved (screen tearing less visible). I got a Samsung Syncmaster P2450H on VESA wall mount so I need the same lenght and wall mount to replace it. It a wonderful monitor anyway, it will be hard to give it away to my father