I did some S/F speed trap testing during the race:
GT1:
R.De Jong [XRR] 166mph
S.Fischer [FXR] 164mph
E.Liibeon [FZR] 165mph
So yes, in GT1 the FZR is slower on a straight.
GT2:
P.Diaz/K.O'Keefe [XRR] 153mph
L.De Jong [FZR] 151mph
G.Alamaras [FXR] 151mph
Again, FZR slower than the XRR on a straight.
Of course these are all variable by set/lap/driver or whatever, although they were fairly consistent lap by lap to +/-1 mph