I've got this dilemma as I have tracked the S1K and had a minor off (which cost lots to put right, even with the crash bungs) I've also got my old ZX7R sitting doing nothing - strip that of the road gear and it makes a really useful track weapon - quick enough to have fun, but stable enough to learn. Problem being that 7R prices are starting to firm up, so there's also the option of getting it back to showroom standard and flogging it, as it's not leggy...
One thing a racing mate said was that I'd learn more on a slower bike (he was talking a 600) to begin with, rather than just blatting round on the S1K, horsing past people on the straights. Then I could use the S1K properly after getting the most out of a 600 on track. It's pretty logical, but then again it seems nuts to have a bike you can't realistically wring out very often on the road without landing yourself in the cells, and not track it...