Virtual functions are supported, and we have both an existing game and an active project that use virtual functions bound to the JIT. Could you provide an example of the function that is causing the issue, and the way you bound it to AngelScript?
As for performance, unless you are regularly calling functions that can't be directly JIT'd (we fallback to AngelScript's calling system), there should be at least a doubling of performance. Again, it would be helpful to have examples to go off of to see why you might be getting poor performance. Without scripts or code, I can only guess at what is wrong.