Everything about it looks great (good numbers) except it only has 512mb of video memory. My monitor is 1680x1050 and I've been told by some sources that 1gb is only needed for higher resolutions, but I've also been told that 1gb is needed to run some games on ultra settings. The only games I have in mind are Starcraft 2 (which I would like to run on ultra) and future MMOs. There was a Starcraft 2 benchmark article from this site but it only referred to higher tier cards not within my budget.
So I'm really not sure whether the 512mb will do or should I aim for one with 1gb like this HD 4850:
First off, you can't directly compare clock speeds between Nvidia and ATI cards, hell, you can't even do it between different cards from the same company. Case in point, a 5850 clocks at 725mhz, and my 4870 clocks in at 750. There is no doubt that the 5850 is a vastly superior card. Each company and card model has different architecture, and will perform different levels of "work" per clock cycle.
I ran a single 4870 512mb for a year before getting a second one very recently. 1680x1050 was the resolution I would usually drop to if I couldn't max out a title at 1920x1080. Granted, the 4870 it is a stronger GPU than the 4850 mentioned, but the need for extra video memory can only be determined by the the GPU's ability to actually utilize it. Having more video memory than needed performs the same as having enough.
I would consider the 4850 the starting point for GPUs that can use more than 512mb of video memory. For your budget (100-140) a 5750 might be best. It will perform the similar or better than a 4850 while using a lot less power, and can be had with 1gb memory for some piece of mind in that arena. Not to mention that the 5750 uses GDDR5, which itself makes a big difference from the DDR3 on the 4850.
I saw a benchmark, I really can't remember where, and basically the difference between 512 and 1gb in terms of FPS was minimal until at least 1920x1080 and at highest resolutions it had a fair impact. Still, as these guys are saying I'd look for a newer card in the same price range.