Will the PHAT shaft do the same as a balanced set of TWINS? I'm not sure. To that end blowing lots of black is either for show (sometimes fun), unburnt fuel (can get pricey) and or a low boost condition.
Further to that, I have direct exp. with the TST products so I can't comment on that. I would call them (or where you bought it) and ask them what they think. Ask them, if I do "Y" can I get it back to "X" or even "stock" if something goes wrong or you don't like it? If they say no or give you a deer in headlights glazed look then I wouldn't do it but hey that's just me.
All I know is a SMARTY on level 7 smokes like blacker then the ace of spades when you start in second from a dead stop at high elevations (I was in Calgary when I got to play with it). Living at sea level I can't say what it would do but I'm assuming it would smoke a bit less. I also know that having a SMARTY set to 5 in a truck with TWINS and a EDGE comp and some 275's goes VERY fast!