I use 400 for everything with my DFP, I've tried more lock but TBH it just highlights the force feedbacks slowness and at 900 degrees it's really annoying to drive with high FF settings because the wheel reacts violently not able to keep up with the cars natural desire to pull straight, at larger rotations it's possible to get the car to loose control in a straight line.
Real drivers probably use something around 540 degrees in production based cars and nearer 400 degrees in purpose built cars. Generally I think the lack of precision with a smaller lock isn't an issue and is more than made up for in RL and in LFS by the ability to steer faster and in LFS by the reduced FF lag as well.