Someone tell me why I should go with the 250 over the 4850.
Price?
Remember that the review I provided was an OverClocked 250 that allowed it to perform "in the middle of the 4870 and 4850". Pound for pound though, BOTH overclocked, or not ... they are fairly identical in performance.
http://www.tomshardware.com/reviews/geforce-gts-radeon,2274.html"If you skipped over the article to find out if there’s a clear winner between the Asus EAH4850 MT or the Gigabyte GV-N250ZL-1GI, I’m afraid you’re probably going to be disappointed. Both have a great deal of strengths, a few weaknesses, and on average very similar gaming performance."
They do note a very slight performance lead "IN THE GAMES WE TESTED", to the 250. But this 250 is also a 1GB card where the 4850 was not, and whether one could actually visually measure this difference in real world use is debatable. Call them the same (as they do), and look for the best price.
With that out of the way, (and without knowing your system specs), what about the 4850's replacement in the newer Radeon 5750?
http://www.hardocp.com/article/2009/10/12/amd_ati_radeon_hd_5770_5750_review/1"Compared to the GeForce GTS 250, which is also at the same price point, it (5750) varies. In some games the experience will be the same, in other games the GTS 250 may perform better. If you already have a GTS 250 there is no reason to upgrade unless you need DX11 support, and the fact is that you just don’t right now. If you are debating between these two video cards, we would learn toward the Radeon HD 5750 in light of its forward looking DX11 support, ATI Eyefinity support, and greater power efficiency."
Here is a
comparison of the 5750 and 4850 (amongst others) and the 5750 can generally give a few more FPS over the 4850.
"in the worst-case scenario it achieved the same performance as Radeon HD 4850, being on most situations between 4% and 13% faster than this previous-generation video card. On situations that high-performance is needed, in particular on Far Cry 2 with image quality settings maxed out, Radeon HD 5750 achieved more than double the performance from Radeon HD 4850".
The newer 5750 will likely cost a little more though; Newgg lists a
few 5750's starting at $145.
You can get a general
overview and feature list from AMD. If you have Windows 7, or plan on it in the future ... I would look at the 5700 series cards, otherwise -either- the 250 or 4850 would be good choices.