RE: 46 engine comparison
The SF is a great engine and will last for a long time. Unless power is an issue, I'd leave it be.
The AX and TT .46 Pro are my pick of the modern engines too. They are both very consistent (each engine performs and throttles much the same) and are amongst the most powerful mass produced sport .46s available.
The AX is slightly more powerful than the TT (12.3k versus 12k with an APC 11x6) and both will pull about 1000 rpm more than an SF with an APC 11x6.