Five speed box

Most 5-speeders I know of has a higher 1st than the standard gearbox. Makes it a bit more impractical in traffic. What you really want is a wide ratio gearbox that gives you a low first for slow going and a tall fifth for keeping revs down when cruising. Sadly I don't know of anyone. My only experience is of TTI and Quaife for racing. There they makes it easier to keep the engine in its narrow power band.

Mike

If we were to get a 5Th speed would it be direct drive? , this would mean that most of the riding would be in an indirect 4th with the subsequent heavy wear on the sleeve gear?? And the need to fit a bigger box sprocket to get an overdrive effect ,which would mean all the gears ratios would then be raised, or need to be lowered to compensate?.  Not simple.

No idea how a Quaiffe cluster would go on an 88 but I fitted a new 5 speed gear cluster from Mick Hemmings in my Mk3 with standard 4.38 gearing and Castrol EP90. 

This was around 20,000 miles ago and I would never refit the 4 speed despite many comments on various forums about there being no need for more than 4 gears. The torque doesn,t compensate for the gaps between the gears from my experience and that same torque with decent ratios is way better.

It's one of the best mods for trouble free riding enjoyment on my bike. First gear is higher but no problem with 850 torque and certainly doesn,t make riding in traffic more difficult. 

Ask Mick Hemmings about the available Quaife first gear ratios and suitability for an 88 with a kickstart. That would be the only consideration apart from price. I suspect it would make riding your own bike a much nicer prospect especially if you enjoy riding roads with many corners.

Top gear is direct so that will be the same as standard assuming you have the original sprocket and tyre sizes, no need to worry about sleeve gears!

I can see that a closer ratio box  would make an 850  a pleasant ride and it would pull the higher first gear no problem . It already has a fairly high top  so maybe does not need a cruise 5th anyway and with the Isos does not vibrate at 75mph.. The 88  will struggle with a higher first but can cruise at 75 as its a smoother motor . The 99/650/Atlas  are the ones  that really need an overdrive 5th  to allow comfy 75 mph cruise as the vibrations are greater. A close ratio box will not do the job.