Hmm, this is interesting. I only have a P233 but I should be apparently be getting at least several times faster than an A4000, rather than crawling along (20 seconds to layout and draw a simple AmiDock dock, for example). I could do much more programming if my programs did not take 15 seconds to open their main window, etc...
I did try this JIT but it doesn't seem to work for me, I hear people saying how fast it is but I don't notice any increase? Perhaps someone should write something on how to set JIT up so it actually works.
Because when I tried it, it was so slow that I went back to using WinUAE 0.8.9. And, as I mentioned above, I get about A500 performance at best on that, so the performance of later WinUAEs is even worse on my system.