I really have no idea whether Tact or Pool gets you going faster here, but I'm leaning towards Pool. If Tact does start up faster, I'd guess 1-2 turns faster at most, but Pool will give you more draw than the Lab stack, which gives better guarantees in the endgame. The ability to for example use Stonemason on $6+ costs to get as many Cities as you can, then draw them all with one Pool is nice.
I think ideal play here is that you go for Pool, then use Altar to get 1 Tact at some point. You use the Tact more for the +Buy than the extra cards.