I've been doing some research lately and it looks like 1.9.3 is about 20% faster than 1.9.2 and loads the VM and libs about 30% faster
No idea if it will be a problem to embed never looked at that.
I just haven't had time to set up a convenient way to be able to update and build Ruby whenever I please. Also, I barely remember the few fixes/changes I did on the source, because we had some problems with it. If you remember, there was the bug with "changing" the superclass of a class when you redeclare it. I may set all of that up when the are close to the release.
ah, well it's not like it's urgent, I sure ARC will be plenty fast as it is just something to keep in mind for release time or if it proves to be a problem then a future release.