I agree on the Yak for competition and the 580 for practice. When I say 'practice' I mean foolin' around or learning a new maneuver where you don't want to risk your big ride. But if you know the maneuvers in your schedule, then I would fly the Yak extensively, maybe even exclusively, get it trimmed to your complete satisfaction, so flying it becomes second nature. Check the IMAC website for the Peter Goldsmith trimming procedure.

I own about a dozen YS engines, have set them up with pretty much every brand of tank in general use, including a few cheap ARF tanks, and never had one split on me. I have heard of such things, but never seen it. Don't be afraid of the YS, it's a super sweet performer, but absolutely 20/20 fuel to get decent performance from it, on up to 30% nitro after you fall in love with it. The YS loves an inverted mount. Get yourself a Venus (the original, not the II) or a similar 40 size pattern model, put the YS in that, and you'll have a very capable small model to practice your IMAC routines with. My Venus with YS53 and YS63 provoked more spectator comments & questions than anything I've ever flown.