I looked at this, but the stop the world GC would still kill the frame rate from time to time sadly. Also there's a large amount of inefficiency in the object translation layer between the two languages.

I can believe that, but wonder if it needs to be so.

For example, in my (limited) experience, you have to draw the boundary between what's in Ruby and what's in C/C++ intelligently. If you're still doing most of your computation in C on Ruby Arrays and Hashes, you're not going to get much of a performance win at all.