Nigel, stock gearing gives 100 MPH at 4600 rpm in top gear. This is with a standard 19" rear wheel , 21 tooth sprocket on the transmission output and 46 teeth on the rear sprocket. The 4600 rpm at 100 MPH number is either from Rider's handbook or Richardson, I forget which, but it is an accurate calculated number rather than one with speedo error.
Quaife offers two first gear ratios, one very high for racing and one that is close to standard Rapide for road riding.
Sounds like you have the racing first gear. It is similar to the early Black Shadow first gear, which was also a bit high for road use.
Quaife has also changed their fourth gear ratio. Until a few years ago it was 1.07, hardly any change from fifth at one to one. It seems this was racing inspired as well. For the road it makes little sense to have a five speed with essentially two top gears.
Customers must have complained because fourth now has a ratio of 1.15, much more useful.