I was using Flightpower EvoLite 5350 mah packs in 3s config. I did not constantly gear for 55 but it ran fine when I did. I kept it geared for 43-45.
I ended up having to get the traxxas extended hold downs for the batteries to fit. It was still tight but worked.
http://www3.towerhobbies.com/cgi-bin...?&I=LXTKN7&P=7