You should be fairly close with the stock carb jetting. E10 pump fuel does make a difference but, it's pretty difficult to go too far afield anyway, as long as the carb is clean and in good working order. The stock setup is quite forgiving. Typically you'll have three jet needle height settings that deliver okay throttle response & performance. It's the Goldilocks thing...one will be a bit too rich, one a tad on the lean side and one will truly be best. The changes, between two adjacent clip positions will be quite subtle, to the non-expert tuner. But, with a little practice and some experimentation you'll catch on.
At most, you might want to upsize the main jet, going one step larger. That said, I'd start by checking plug coloration; that should give you a fair idea as to where you are at present. Next step, successive test rides with the jet needle C-clip in the lowest groove (richest setting) and topmost groove (leanest setting) at least one of those settings should deliver a really bad result...either too rich or too lean. If, as you suspect, it'll only go too lean, then it's time to order up the next larger size main jet and retest.
Going by your "tons of power" comment, it seems that you're not running seriously lean. Overly rich mixtures deliver WOT misfire, black exhaust smoke and, if the pilot (idle) circuit is rich, too, overly-easy cold starting, sans choke. Lean mixtures usually mean difficulty with cold starts, having to keep the choke applied for long time until the engine & intake manifold warm up and stumbling/bogging with enthusiastic throttle application.
I'll check to see if I have any of those dipstick thermometers left.