5 Speed gearbox or a Lower Ratio Diff??

[buck]

I have a wb 253 with 3.08 diff ratio, its is doing 2600 rpm at 100klm, i think you have got a 3.55 diff which my old hz had and it was around 3000rpm at 100klm.
3.08 is perfect for 253.
my mate has a 5 speed supra with 253 and 3.08 diff , 2000rpm @ 100klm fine for hills dont have to change down, just depends what your 253 is like, mine could easily handle a 2.78 diff, as it around the 140-150 kw mark.