What plane you gonna use this on? For torque the Irvine-53 is awesome...
I have to admit Bill, my OS-50SX is great runner, and it is ringed... I would never pay full price for one (got mine in a trade-) but it has handled a 13x4Z to a 10x8 APC

flip starts and has not dies yet!
I also have a K&B-Screamin' 48 and it does scream--- great engine!