Ran 14/39 on the 996 and it was a lot better than the 14/36 set up.
With the 998 I ran 14/36 instead of 15/36 but it has so much more bottom end it pulled it real good but never tried it on track.
With the 748SP I have tried 14/41 which was ok but on a lot of corners it fely half a gear too high or low so went to 14/38 and had the same results but a lot of corners were carrying different gears through em and bogging on the exits. Settled for 14/39 same as the 996 and it was a lot better, pulled ok out of corners if you kept the revs up and also once up to speed on the straights it was keeping up and catching other bigger bikes as it could use the top end of the rev range where the power is produced.
Trial and error so get a quick change sprocket carrier, it works out cheaper
I know Jasper went the other way with a 15 front and bigger rear sprockets on his bikes to keep the wheel base to a longer length but had to alter his ride height a lot me thinks?