4th gear seems to run out of steam about 60mph where dropping into 5th makes it fly (if a 1ltr can) again.
thats right wierd unless either your dials are badly off, or your wheels are tiny and you've recalibrated, or both........

personally if i'm looking for speed in my own (
supposedly having same 1st 4 ratios as yours, and same engine) i'm not even getting
into 4th from 3rd until 70-75mph, let alone looking for 5th at 60... if its what i thought it was, then 5th should give less pull than 4th, end of story.. unless of course it's just the feeling and sound of it because it's at maximum grunt at 5th around that speed
are you absolutely certain it's not a GT box and your speedo isn't reading slightly high/tacho slightly low?

pretty decent to be getting 90mph with it only pulling 4500rpm though, by rights there shouldnt be enough power there unless the actual curve is a lot nicer than i'd hoped! (still getting >50lbft at 4500... bonus!)
If it's the same one fitted to mk2 1.3's with the 4+e box, there are two in my scrappy atm, I'd happily get you a price for one

thatd probably be the ol' 8P which now seems to be too high geared for my purposes... having a higher rather than slightly lower 4th isnt quite what i'd hoped

still... if it's intact... not too pricey... and i can find somewhere to offload the polo whilst still being the owner/keeper (and getting something else in the meantime) it'd be cool to play about with trying to swap the differential reducer gears while it's effectively SORNed.
(especially if the "smaller" 4sp pinion can be made to work with the "larger" 5sp ring - slightly shorter and non-VW spec 4.333 final drive

)
I'm -really- happy with the 5 speed box I've got in now.. don't know the code, but it's from dubs' mk2 1.0 classic, I think 5th is about the same if not a touch higher than my old 4th. I get 70mph at around 3,800 rpm
GT-style box mate, the shorter geared variant

(the actual gt was a bit taller all round)
at least i can still I.D. THAT with some certainty
....ish
a price would be appreciated but not if it'll put you out.. want to concentrate on e.g. getting the stoppers sorted first