Yes! Here we are, the inevitable repeat of the ATI 5850 vs nVidia GTX 470 post.
I upgraded my monitor (2048 x 1152 res) this past Christmas and have been thinking of a GPU upgrade (from an 8800GT) for a bit. I've been on the fence (and I'm still willing to sit here for a little) waiting for Fermi to see how the GPU field plays out. And unlike some, I think the GTX 470 came out strong. A little hot and the drivers premature, but eventually I think driver updates may let the 470 pull ahead of/match the more mature 5870. Hopeful thinking, but I think possible.
I'm currently running an Intel E8200 OC'd to 3.6 with 4 GB of RAM. The mobo has an Intel P35 northbridge, giving me a PCI-e 1.1 16x slot(like a PCI-e 2.0 x8 slot), so I wouldn't expect a major bandwidth/bottleneck problem with either card.
My main concern will be running Star Craft 2 maxed out, if you have a beta key chime in with performance. I have no brand loyalty (Matrox, 3DFX, ATI, nVidia, I've used them all) and I'm just interested in the best GPU for the $$$. I also want this upgrade to last me 2 ~ 3 years before I do a complete re-build.
I'm currently leaning towards a GTX 470 since it has a little more power, but I'm not shy of doing a little OC'ing and letting the 5850 run on some of the non-reference cards with better cooling. Price between the 2 is a moot point, I'm just curious about the performance people have gotten out of either card.
Even though I prefer ATI a bit more than Nvidia, I would say go for the GTX 470, it has a tad more V-Ram than the 5850, which is good for your high resolution. Also, I assume you are using a CRT with that resolution, so I imagine that getting two more for eyefinity is not exactly an option, so that takes away one more point from the 5850's features list.
However, if you get a 5850, and can find a great aftermarket cooler, and possibly one with the ability to volt-mod overclock, it would be very hard to pass up a great card like that, because the upside is so great.
On the other hand, the GTX 470 will no doubt benefit from future driver updates, and can overclock like a champ with extra volts, however I don't beleive there are aftermarket coolers out yet for the Fermi series. Not to mention the Fermi series is going to be hard to get hands on for the forseeable future, so if you want a card within the next couple weeks, again, you must go with the 5850.
There is alot to digest here, but I think you can't go wrong with either card, assuming you can get your hands on one or the other.
But again, I think the 470 is right for you. (espescially if Physx holds any water with you.)
Since you wish this to last you 2-3 years, the 470 is a tad more powerful then the 5850. I have been using the 5850 for a bit and found it to be an excellent card. I like that is has a lower power profile then the 470. On the flip side, NVidia does provide Cuda and Physics which can come in handy now and then.
All in all, its up to preference as both of these cards are so similar and SC2 does not have a high graphics demand as ct1615 stated.