Thought I'd report back on this, or actually have been meaning to.
I finally just decided I'd get a good stand-alone trimmer and bought an Echo SRM 225. I'm super happy with it all around-it definitely feels a better quality piece(even though I know it's close to the least expensive Echo you can buy) and just feels unstoppable even though I've only used it a couple of times so far.
Meanwhile, the dealer actually included a can of Echo brand fuel with it. He insists it's the best out there(better than Tru-Fuel) but whatever the case it was "free" and it's all I've been using in it.
I threw a little of that in my old Ryobi, adjusted the carb, and it seems to be running better. I'm not sure how much life the trimmer head had in it either, but I'll keep it around and it seems to be fine running the pole saw and hedge trimmer now.
So, I'm happy is all I can say!