Peter,
go the 3", they are far more comfortable and in case of the unthinkable, spread the load more. I had a very high speed crash in a different car with 3" belts... bruised but not broken..
I think I have the same set as Leeroy. They are permanently in the Car, so check them out at the Drags next week.
Leeroy, you might find if you really pull the belts tight, you won't get soreness. It can be from the belts being a little loose and your body getting pushed around. It's amazing the forces that get applied. I have mine tight enough that even in the corners I am only lightly holding the wheel.
Cameron