The 7950 does indeed deliver slightly better performance when v-sync isn't used, but it's not a massive difference on average and nVidia gives the advantage of adaptive v-sync.
V-sync (as in standard v-sync) is a technique used to manage framerates, so that if your framerate exceeds your monitor's refresh rate (typically 60Hz), you won't experience screen tearing. All cards support standard v-sync. The drawback is that if your card drops below 60fps, even just slightly, the framerate will be significantly reduced by v-sync. If your framerate drops below 60fps and you leave v-sync enabled to prevent tearing, standard v-sync (Radeon) will reduce performance, while adaptive v-sync (GeForce) will deliver smooth, fluid performance, since it won't restrict your framerate like standard v-sync does.
"With Adaptive VSync turned on, the feeling of the game felt smoother compared to regular VSync turned on. The performance felt much like the game felt with VSync turned off. This is the kind of technology we like to see which has improved the innate nature of the gameplay experience. If all you need is 60 FPS in a game for it to be playable, then why not just go ahead and cap the game there so it doesn't exceed your refresh rate. Then, if the game has to fall below that, allow the game to perform at its real-time actual framerate, and Adaptive VSync allows that. It really is the best of all worlds, with no drawbacks. We didn't find any negatives to using Adaptive VSync, and we tried it out in a handful of games."
If you go with the 7950 despite that, it would be good to grab an MSI or Asus model. Coil whine is not nice!
I was almost gonna suggest XFX but I'm not 100% sure about the quality... I have one at the moment and I think the fan bearings are shot - pitch is constantly up and down and when the card is cold during boot, it's like a diesel engine. To be fair, it's a couple of years old now, but made me hesitate to recommend them.