Novak 4.5 or MM & Fiegao 8XL in G3R w/ (2) 2s2p for 4s

[suicideneil]

2s lipo is 7.4v, so 4s is 14.8, not 16.8v (you're thinking of 7 cell nimh packs).
Anyway, if the 4.5 runs fine once its back with you, then I see no real point in spending yet more money on a new motor, esc & ubec really- like you said, you just have to gear the hv4.5 abit more carefully, and it really does run great on 4s, a very fast and quite powerful setup. The 8xl would be even more powerful, but then again it would also be quite hot after a good run- depends on how much torque you really want, since the hv4.5 will propel that Revo to 40mph with no real trouble, especially when its fed good lipos like yours. Thats my opinion anyway.