Well.. our Polaris isn't much different from your Eton... Polaris doesn't make their own mini's... they are made my Aeon for Polaris... very similar in design to the Eton and Kasea minis.
I wouldn't got for a yamaha mine.. the front suspension is garbage. the hondas are nice, but I prefered the performance of the 2 stroke minis over a 4 stroke.
As for you eton in need of a top end.. now would be a good time to upgrade to a 70cc kit for that quad... you can do that the same as rbuilding a top end on the 50, you just swap in a new jug and piston. (about $190 or so)
For someone closer to you in Texas, contact Peak Performance in Rockwall, TX.
http://www.dirtrides.com
Bryce