The 748R is higher geared compared to any other 748. In this case, by gearing, we are really talking about sprocket sizes and ratios.
748R standard 14/36, 748SP & SPS 14/37 all others 14/38.
Sure the bike feels "OK" with standard ratio but "OK" could be better! The cheapest option is to source a good secondhand 38T rear sprocket from another 748. Your other option is to by a seperate rear sprocket carrier to which you can then fit a wide selection of sprocket sizes. More expensive due to the initial outlay for the carrier (£85 - £135 depending on which brand you go for) but the payoff is that the sprockets are cheap (£25-£35).
Even changing to a 38T rear will make a really noticable difference although if you go down the carrier route maybe think about a 39T or 40T.
As the 748R more than any other Duc thrives on revs, going up at the back helps to keep the motor in the "sweet spot". You lose a couple of mph flat out but no more than that - when was the last time you had it flat out in top for any prolonged period anyway?
All I can say is DO IT!!!! Transforms the bike into how it should really have left the factory.
Cheers, Neil.
P.S. If you go higher than 38T you also need a new chain - up from standard 94 link to 96 link.
True, one tooth off the front is generally pretty close to adding 3 at the rear.
Dropping from the stock 15T to a 14T front makes a huge difference on a 916/996/998 and costs very little to do, however, in Phil's case he already has a 14T on the front so that's not an option.