If you stick to LFS then you'd say most cars have 720 degrees of lock. I read that a real Porsche 911 (dunno what year) has 1080.. Most road cars seem to have at least 900. I like that LFS actually shows the graphical wheel turning more than a tiny bit (as in most other sims, they don't turn enough!) but I wouldn't say that 'realistic' is to copy the rotation you get in graphically in the sim. I'd more look at what their real life counterparts would use. GPL and N2003 have wheels turn about 320 degrees, where in real life a GPL car might even turn ~600+.. In RBR for instance the graphical wheel turns only about 30 degrees..
The problem with a DFP type wheel is that they have roughly the same gearing (wheel to motor) as a MOMO, hence they have about the same 'top speed' when the motor tries to turn the wheel. Now you go max left to max right, the wheel with more rotation will take a longer time. So MOMO type wheels with say 240 degs of lock go lock to lock 3.75 times quicker than a DFP at 900 degrees..
From various videos, even 'road cars', it is obvious that due to caster, once the back steps out, the driver can simply let go of the steering wheel as the front wheels will keep pointed in the direction the car is going. This can be some seriously quick turning of the wheel. If the wheel can't do this quickly enough, this 'driving aid' (well its 'real' but it helps greatly) becomes an obstacle as it doesn't steer quickly enough..
So instead of what you'd do in real life, i.e. let the wheel slide through your hands, ready to grip it and adjust it slightly, you'd have to try and force the opposite lock. You then encouter a good amount of resistance as you try to spin the motor at a few 1000rpm faster than it can.
The gearing from wheel to motor is about 1:40 .. so for each rotation of the wheel the motor turns 40. The max speed of the motor is ~2400rpm, although that is hard to say with a load on it, might be quite a bit less. In 'free air' its probably faster than 2400. Logitech use 40:1 gearing because that also increases wheel force by 40 times so they don't need a big motor to develop big forces. They don't care about speed..
If you steer very quickly you can certainly reach a speed (not constant but a quick 180 degree correction, keeping your hands on the wheel) of about 3 or 4 revolutions per second. that is 240 per minute. Times 40 is 9600RPM on the FF motor! The motor does NOT like this and that is the resistance you feel trying to steer fast with a current day FF wheel.*
So realism would be letting go of the wheel as it automatically applies opposite lock. With a DFP at 720 or 900 degrees, especially with 'snappy cars' like the lx6, you can TOTALLY not get force feedback the way it would be in real life. The wheel can't keep up.. You end up doing the opposite of what is realistic: you try to force the wheel where it should go by itself! Of course opposite lock / powersliding is far more than just letting go of the steeringwheel but its a good example to point out where big rotation big gearing wheels like the DFP are so bad.
In 240 degrees mode the problem is less but then again it is unrealistic to keep your hands on the wheel wich such a small amount of lock..
*SHould be better with the G25..