K1,
My opinion 4-stroke is the only way to go. The only other thing is don't be afraid to go to the top of the engine range. Here is why... LIMITS!!! The big vs the little saga... If you go small that's where it ends. If you go a little bigger that engine will apply to other airframes. As you already know this hobby is addicting. Furthermore if you plan to eventually grow into other planes it would be nice to have some single purchases instead of many. The 52 might be cheaper than an 80 but your most likely gonna buy that bad boy anyway. Remember you can't use the altitude above you, the runway behind you and the power in the engine you didn't choose!!!