Me. UAE-X is good, but the lack of CAPS support. The speed of emulation in high compatibility mode is sometimes below 100% A500.
The biggest problem is that the majority of Amiga screen modes were what is called "Single Field, Non-interlaced". It is likely that the X-box can do such modes, but they are not supported in the X-box SDK.
As such all modes are promoted to interlace and flicker