Jap Import

Hi people, my box has recently blown on my 94 Type RA.

5th is missing almost every tooth, damn.
It's proving really hard to find a 5th the same ratio as I have already.
I have the chance to add a taller 5th instead.
I know allot of RA owners do this but I dont want it to drop so much going from 4th to 5th.
Whats the difference like?
I dont really do allot of motorway driving but at 80MPH it's around 4500rpm, so I do get a little concerned.
I'm not too excited about top end in a car, never have been.
It's always been about 0-60/80 for me.

I'm really after your thoughts, before I decide.

Thanks in advance