Quote from Skuzzy when i was trying to get my card settings adjusted. So i guess if you're still looking for a card in a certain price range, and AHII is your main game, then these are two things that you can use to measure one card against another.
The single greatest video card specification in determining performance is memory bandwidth expressed in Gb/s which is directly tied to memory type (DDR2/DDR3, etc.) and memory speed (expressed in Mhz). Unfortunately, this is not a spec that's listed on the retail web-sites but the memory type and speed typically are. I'm not sure about ATI but eVGA does list this spec for all current products on their web-site. Pixel pipelines are also important as I'll explain in the first paragraph below.
For the stock 9500 GT, 9600 GT and 9800 GT their memory bandwidths are 25.6 Gb/s, 57.6 Gb/s and 57.6 Gb/s respectively. The substantiating difference in the 9800 GT over the 9600 GT are their 112 vs 64 pixel pipelines respectively. Pixel pipelines affect pixel and texture fill-rate which is important in 3D applications/gaming by increasing the pixel/texel per clock performance. If the applicaton you are running isn't 3D, the 9600 should give performance similar to the 9800. The price differential is about $20 as you step up from one of these cards to the next so the 9600 GT provides the best value from a price/performance perspective for normal computing but the 9800 is a worthy upgrade if gaming.
When comparing similar cards, the 9800 GTX, 9800 GTX+ and 9800GTX+ Superclocked, the memory bandwidths are 70.4 Gb/s, 70.4 Gb/s and 71.8 Gb/s repectively. The 9800 GTX and 9800 GTX+ both have effective RAM speeds of 2200 Mhz although the GPU clock on the 9800 GTX+ is 740Mhz vs 675Mhz for the 9800 GTX. Obviously the RAM speed is the limiting factor between these cards. I'd expect performance to be similar but the GTX+ should be able to handle slightly more difficult processing. The 9800 GTX Superclocked has a faster GPU (756 Mhz) and faster RAM (2246 Mhz) and should be the better of these three cards. The price differential between these cards is only $10 as you step from one to the next. and the statistics bear this performance difference out. Tomshardware shows only a 3% performance gain in FPS (3Dmark) going from the 9800 GTX to the GTX+. If it were me I'd save the money on the GTX+, buy the GTX and overclock it myself. If you're not comfortable doing that then spending the $20 for the factory overclocked version is a reasonable price to pay.
Finally, as we look at different memory configurations the 9600 GT 512 and the 9600 GT 1024 both have GPU clocks of 650 Mhz, Effective RAM speeds of 1800 Mhz and memory bandwidths of 57.6 Gb/s. Performance wise these cards should be very similar unless you are using V-RAM intesive programs or proccesses (video editing, etc.) at which point the 9600 GT 1024 makes sense but for $45 more I'd want to make sure that's the case (AH won't use that much memory; 512 Mb is certainly sufficient).
These particular cards were used only for the purposes of providing examples. Finding benchmark tests to substantiate what you think the stats are telling you is always a good idea.
[EDIT] Of course I could be wrong but those are my observations.
