Hi
I have an MVVS 91 but have yet to run it.
It is a very well made engine as it reputed to be an animal if run in carefully.
It is a longer stroke engine than the OS so it should throw a bigger prop.
I am told it is more powerful than the OS .
Do a search and you will find no end of threads on the MVVS and no of them had a bad word to say about the engine.
earlier version had carb problems but this seems to have been addressed.
Bare in mind the MVVS is not some cheap eastern European paper weight they have been in business since the 50s and have won alot of speed titles so they know how to put an engine together.

Mike

ps i am running mine on a pipe and a perry.