Hi guys, first post !
I have a 200 and I run 50:1. I bought the bike and the engine was rebuilt (along with the whole bike). I have had it now just over a year and I have no evident piston/barrel wear and the bike is a little ripper (probably something to do with the 51 rear sprocket..hehe)
I use the Castrol TTS or silkolene synthetic, depending on which shop I end up going to.
I also run the NGK '8' plug , a little warmer. It never fouls plugs.
I only changed it this time due to stripping the bike down (pre winter riding) and replacing consumables.