Anything in the 10-15% nitro and 18-20% oil range will work fine...I've got 5 Evo engines and they all run great on either Powermaster or Omega fuel. I like the H9 Super Plug that comes with the engine or a "warm" long reach plug.

It does sound like it is rich through the transition...and you might need to re-set the "Set-Right" collar to allow you to lean the low speed some more? We usually just eliminate the collars because they get in the way and are a PIA.