Luizinho:

Here in Malaysian my friends are flying 2 Kyosho G trick, 66" patterns. ONe uses an OS91FX with bolly pippe. The othe uses a MVVS 91 with mini-pipe.

I tune and adjust both planes from my 2 friends.

Here my honest opinion.

The MVVS is :
as easy to tune as the OS
seems to fly the plane faster.
vertical on both are excellent and you will not want.
MVVS metallargy is definitely superior and will almost definitely outlast the OS
MVVS can use lower nitro
OS Is a btter looking engine.

verdict: it depens on what you want. .. I plan to buy the mvvs bec here it sells for US110 and the pipe and manifold is only abou 30USD!! OS is bout 50-100% more!!
btw the MVVS 91 seems to like a 13-8 or 14-6 apc. spins about 12K or first and 9K on second