I would do the Go 5 port turbo before the .28 jpx. Out of three of us running MBX5t's last year I had the Go and my buddies one ran the ofna p3 .28 and the other the jamming .28 they were lucky to get 6.5 min. on a tank. As for me the .21 motor was almost as good on the bottom but better on the straight and much easier to drive faster and more consistant. PLUS I GOT OVER 8 MIN. OF RUN TIME!!! As for the .25 I haven't seen one so no idea?