I'll bite, what are the timed benchmarks?
Are there any benchmarks that UAE doesn't "optimize" right out to the point of being invalid?
I can say this, though. UAE seems to hit a ceiling on faster machines. I have a P4 3.0C edition with 1GB of OCZ low-latency DDR-400 set up in dual channel mode (effective 800mhz FSB). This thing is the fastest single processor Windows/Linux box I've ever seen. (Yeah, yeah, I know the 3.0C has the HT option that SHOWS two processor fronts to the OS, but it's still a single core...)
Anyhow, WinUAE doesn't run appreciably faster than it did on my 1.1ghz Athlon T-Bird that featured pathetic PC-133 SDRAM!