If you can, race a friend's GS...and let me know the results. I have seen #'s out there on edmunds.com to be exactly the same for both cars (5.9) but noone knows the real #'s....since edmunds.com show that GS430 is SLOWER than GS400 (6.3) . I think there are numerous factors affecting the outcome which noone seems to take into account (including how fat the driver himself is!!!)