For that matter WinUAE 2.8.27 runs dog slow on my 64bit laptop too, (SNIP)
Probably issues with WinUAE**'s CPU idle detection system...
**0.8.21.R4 introduces "CPU idle patch (no more 100% CPU usage)" feature (I rather have 100 percent override). Sometimes, this detection system causes WinUAE’s CPU percentage values to stay low(e.g. <10 percent)(even IF one do something within emulate ecosystem) thus, slowing down emulation speed.
I have experience this issue with 0.8.27 and 0.9.9Beta1 (occasionally, but rare). I use WinUAE 8.21.R3 as reference.