A club member and I both built and flew "Contenders". He powered his with .61 and I powered mine with the OS-46FX. Both planes flew about the same. IMO, the .61 didn't fly any faster or perform any better than the .46. If he the .61 was better, it was marginal. Having said that, the .46 is a good choice.

Also, build it with flaps. Not much more work, but the flaps adds a lot of enjoyment flying the "Contender".

DaveB