If you want something fast and reliable try a yd85. It's basically an avenger 85. Also the lazy mans saw hybrid. The saw hybrid clones have a good powerband, are easy to modify, and have quiet a catalog of parts. You could do what Gordy said and do a saw hybrid. I just finished my first one up and it's a blast! But it takes a lot of time to make, requires a drill press (sort of), its REALLY easy to screw up, and needs a lot of supporting mods to make reliable.
I've been looking into easier saw conversions and for a while I've been wanting to try the ms380 cylinder with m8 to m5 thread reducers on a yd100. The ms380 has the same bolt pattern as the yd100 being 50x50 but they don't share the same bolt size hence the thread reducers. Plus you'd have to still take the thing apart and balance the crank and upgrade your clutch spring.
Or yah know, minarelli's are starting to get cheaper now and pipes are starting to become more available.