I've tried starting AS with the two implementations, and the overhead of creating accessor classes means javassist is slower.
Javassist: ~24.5s
Introspection: ~21s
I need to profile this, but think this is because when configuring beans, we normally only set properties once, so we get the overhead of creating the class, but not the benefit of invoking it lots of times.
I will ask Chiba if there is anything that can be done to JavassistMembersFactory to make this faster.