Acutally, we do spend most of the time at full throttle during combat. While you do turn a little tighter at a lower throttle, that only works for a short turn, maybe 180 degrees or so. You need all the pull you can get to keep turning at high AOA, if you get in to a turning duel with someone, you can go around in circles for quite a bit, so you need a plane that can maintain speed at some reasonable turning radius.

Btw, besides UHMW, there is also HDPE, High Density PolyEthelene. It's the same thing, just not quite as dense as UHMW. It's a little stiffer than UHMW, and almost as resistant to breaking.

The Norvel engine do have the best power-to-weight, but not necessarily the most power. And the Norvels can be a bit hard to get running reliable until you are used to them.