The 1998-2000 1UZFEs are all essentially the same. The GS400 has a better flowing exhaust system than the LS400 and SC400 and the GS and LS have better exhaust manifolds than the SC400. At 3655 pounds the SC is the lightest of the 3 and should have a performance advantage but it does not. With the extra power and 3690 pounds the GS400 is rated quickest from the factory. The relatively heavy LS400 at 3890 is rated the same 0-60 and one tenth slower 1/4 mile than the 235 pound lighter SC400.
Factory ratings are:
GS400, 300hp@ 6000rpm, 310tq@4000rpm, 5.8 0-60, 14.3 1/4 mile, 3690lbs
SC400, 2900hp@ 6000rpm, 300tq@4000rpm, 6.3 0-60, 14.7 1/4 mile, 3655lbs
LS400, 2900hp@ 6000rpm, 300tq@4000rpm, 6.3 0-60, 14.8 1/4 mile, 3890lbs
(mine runs a might quicker)
Based on the stats above I would say the GS and LS are rated correctly but the SC is 10-15hp over-rated due to the manifolds.