Well, I've done some math (actually Excel did...). I do'n't quite know how to put it in words decenlty, but I hope you'll understand. Working with only a TDC sensor will not work at all:

Maximum accelleration:

12000 revs per minute per second =>

200 revs per second per second =>

0,000200 revs per second per µs

At 1k rpm one rotation takes 60.000 µs, so with 0,00002 revs per µs, maximum of 12 revs is added in the estimated revolution following the one at 12k rpm.

At 12k rpm one rotation takes 5000 µs, so with 0,00002 revs per µs, maximum of 1 rev is added in the estimated revolution following the one at 12k rpm.

So a decent 64-1 wheel is certainly required, maybe 32-1, and the thing will need to do the math VERY quickly.

Hugo