From what I have seen, most mid-range CPUs at stock clock end up bottlenecking a GTX 260 or GTX 460 or 5770 at around 2500 on high res and 4500 on low res.
With my 955 overclocked to 3.8-4.0, the bottleneck is actually my GTX 460 (even when the 460 is also overclocked) both on low and high res.
Point taken, though when I say mid-range CPUs I meant more along the lines of older crap like my C2D E6600. I consider a 955 in the lower part of high-range...but that is all semantics.
My C2D E6600 even OC'd over 3GHz will not score higher than 2500/4500 on the benchmark no matter if a stick a 5770, a GTX 260, a GTX 460 or a 5970 in there. So in my case, and in the case of most people just looking to upgrade, spending more than $150 on a card more powerful than a 5770 is pretty much a waste unless they plan on using it in a future build.
Me and my friend have similar builds (i7 930 with 6 GB ram. mine overclocked at 3.5 and his clocked at around 3.9). I am running a an HD 5770 factory overclocked and got around 2700 on high and around 4800 on low. He is running dual GTX 460 (1GB version), but since SLI doesn't work on the benchmark only one of his cards was working. His benchmarks, im otld, were 3789 on high and 6323 on low.
If that's accurate, then there is indeed a reason to pay a little more for a GTX 460.
By the way - anyone want to buy my gigabyte hd5770 super overclocked card? ^^
Another point: I was running the 5770 with my old core 2 duo processor and 4GB ram and the game was playable. AFfter upgrading to i7 930 and triple channel 6 GB ram, it was definatel better, but not by as much as I had hoped. I guess my point is that most people who have a 5770 or better will be able to play... but even if you spend $1000+ on a new system, the game isn't going to be as responsive as FFXI until we get a new generation or two of video cards come down the pipe.
The other possibility is that ffxiv is just not a quick game. What I mean by that is that there are weird little animations when you change direction with your character that try to be too fancy and realistic. your character will stutter his legs and lean his body and flail his arms a little bit as he changes his direction. The effect is that its clumsy moving around since it takes a half or full second to compltely respond.