I have the Sprintbooster (and I like it) - I have the 6 speed tranny, and the Sprintbooster (451 I think), it's a little bit fierce in first gear - ask if there's anyone with the 451A (automatic version) in a 6 speed, it's not as 'acute'.
I would like to get the ECU done, but like you say, it's a few days without wheels.
Get both, I don't think you'll regret either.
$280(ish) vs $600(ish) - your choice!!!