I honestly don't know what the ESC will handle. I know I tried a 13 turn 540 sized motor in it and it kept cutting out, so I would assume it won't handle anything too hot. The whole kit from off shore electrics is around $130 (from memory) and has a motor (Graupner 700 BB turbo), liquid cooled ESC, new prop and the flex line. I don't know how necessary the flex is, the stock coupler "seems" ok. I think the main reason to go with it is to get rid of the driveline vibration. If you plan on modding it, maybe just get the 775 one and leave it stock? Might be cheaper than getting the 550 and then upgrading. Either one will work and you can do the same setups with either also. I am just starting to like the 6 cell setup- I am tired of charging 12-14 cells all the time just to go play . With the 550 and a couple cheap sport packs, I get a lot of run time with little charge time. I may be trying the Graupner 600 BB turbo motor (550 sized) on 6-7 cells. If I do, I will let you know how it works. Later.
Joe