As far as i was aware, the only difference in the turbo gearboxes that changed as time went on is small things like changed syncros, final drive ratios and centre and front diff's etc, like Kami pointed out. But all of the 5 speed gear sets are essentially identical strength wise with the respect to the different ratios as the gears are all helical and the same length.
If you want stronger gears get a 6 speed as the gears are way longer and take a f*ck load more to shear teeth off
If you want somethign that is less likely to crunch as time goes on, get a later box with better syncro design, or dont slam through gears and be nice to it.
The only other thing worth mentioning is there are two generation of 5 speeds, ones that are pre (and including) version 4 gboxs, which have the gearbox code start TY752, which are the 4 point mounted boxes.
Everything after this is 8 point mounted, which means if you want to fit this onto a 4 point block/motor, minor modifications will have to be done