personally, i don't own a big motor, but i have talked to about twice as many people that have problems with mercs as opposed to yamaha. with that said, i do build some large race (car) motors, and just because you can run 8000 rpms, doesn't mean you need to, but you do need to keep it in it's power range, normally 10-12 % less rpm's than its capable of. i service my outboard every other month and have never blown one
150-200hp- i would go yamaha
5-90- i would go tohatsu