Hi mate
There is not much point going too big.
While it is best to have some spare capacity - putting a Bosch 044 into a stock GTS is not very sensible:) On the other hand a Bosch 040 is going to more than enough for 90%+ of modded skylines which have the 'usual' mods.
If you would like to discuss your fuel requirements further, please feel free to email or pm me
Thanks!