The architecture of the chip is completely different. You know how an i7 quad at 2.6 is a lot faster than a q6600 at 2.6GHz? Same idea. More work gets done per clock cycle ... that kind of thing.
The GDDR5 makes up for the smaller bus width because it's quad data rate memory, so 256-bit ddr5@1000MHz is the same bandwidth as 512-bit ddr3@1000MHz (in theory ... in reality, it's probably a little less bandwidth than the 512-bit setup, but not by much)
Comparing 260 to 460, the Fermi cards also have a lot more shader cores (216 vs. 336 ... a pretty huge % difference) and each of those is more powerful on top of it. 460 also has more ROP's than the 260.
In reality if you drill down to the actual important specs, the only one the 260 has an advantage on is maybe texture fill-rate, other than that, the 460 is superior in all the important specs.
BTW, you should never try to compare cards based on the specs you see online, esp. if you don't really know the relative importance of each one. I mean, you can compare two of the *same* cards based on clocks (like an OC'd version vs. a stock clock version), but you can't compare across generations, or across gpu makers (nV vs. AMD) by looking at specs ... esp. not the tiny sliver of specs provided by newegg or some place like that.
You wanna make a good decision, you need to go out and look up benchmarks ... preferably from a few different sites cause some of them out there are biased, either on purpose or they'll accidentally bench a bunch of games that favor one architecture over another.
Then ask on OCN, cause most of us know what we're talking about around here
460 is a nice boost from a 260 ... not HUGE, but it'll be an improvement in terms of your maximum playable settings for sure.Edited by brettjv - 7/30/11 at 11:07am