I've calculated this while ago for PC, but I'm pretty sure it works now on PS3 as well.
If you want to get exact rotation try this formula
100% - [( DD * 100) / WD ] = Saturation settings
where
DD =
desired degrees of rotation (on screen wheel is 250º);
WD =
your wheel maximum degrees of rotation if you can't change it.
ex.
to get
250º on
G27 (max 900º) => 100%-[(250*100)/900]=100-27.7=
72%
to get
330º on
G27 => 100%-[(330*100)/900]=100-36.6=
63%
to get
250º on
T500 RS (max 1080º) => 100%-[(250*100)/1080]=100-23.1=
77%
to get
330º on
T500 RS => 100%-[(330*100)/1080]=100-30.5=
70%
Find out your maximum wheel rotation and do the math. Only thing you will miss out is the wheel won't have hard locks on your set rotation (meaning there will be no resistance at full lock, like on PC with custom rotation and saturation 0%).
If you need more control on straights, don't use deadzone, tune it with linearity.
Linearity 0% gives you 1:1 response, and if you raise it, it makes wheel less sensitive in the middle and more sensitive as you get closer to full lock. I don't have a formula for it, but as mentioned in previous post 5% linearity might be a good starting point.