I wouldn't give up known reliability for anything actually. Is the 45acp something to want and have? Absolutely! If there is any way you can retain your P239 and get the PT145, do it. That way you'll always have something to fall back on, and be secure in your quest. If you have to give up your SIG P239 in order to obtain the PT145, then it's a jump into the abyss for you. Personally, I'd stick with what has never let me down over the unknown. If you don't, you'd be gaining nothing. If you can retain your P239 and get the PT145, then go for it. Otherwise, place your bet on the tried and true.
Now the issue. Do I give up the Sig reliability for the Taurus just to gain 2 rounds and move up to .45?