I mostly stick with 900 for GT5, it took a while but I got used to it(moved up from an old 200 degree DF). 720 seems to work pretty good to get a more stiff feeling, but usually if I'm not using 900 I use 440 so I never have to take a hand off.
GT5 has a very high maximum turn angle so I rarely need to go past what I can reach even on 900, or use it all at 440 - only when trying to save already brutal slides. Having it tighter is probably faster however. The only problem I've seen was the FGT wobbling at 440 with no deadzone, before the recent FFB change on formula cars.
In rFactor I use 440 and adjust the steering ratio as needed, and I changed the on-screen wheel to match.
DiRT 3 seemed ok at 900 at least with slower cars, but even 440 seems too loose for the irritating gymkhana events. I think I used 440 for drifting and 270 for gymkhana. Didn't play it too much though.
I actually had a blast playing Burnout 3 on PS2 with it at 90 degrees when I was testing it with a variety of old games.