from my experience of the 8800GT.
I can run most games with 2x aa with max settings. The only games i have problem running because of my graphics card is Crysis and GTAIV.
The 4850 is better than the 8800GT BTW.
But there are other factors in play, so your results may differ.
I would probably go with a different RAM, preferably one with better Cas Latency. The one you pick is 5 and i would recommend 4. I dont really know why, its just what people tell me to get.
Dont get the Xion Solaris case. I was using that case about 4 days ago, and it pretty much sucks. If you are building a gaming rig, get a bigger case, that case is really small, and it barely fitted my 8800GT, and my HSF wouldnt fit. Which was this one
The one you choose would barely fit, and might have problems with the side fan. The air flow is also bad, my computer ran a bit hotter than my old case.