Are you sure you're in 1:1 full screen mode? I can get higher frame rates if I don't use 1:1 full screen mode.
Once the game starts you need to press ENTER on the numeric keypad and press () on numeric keypad (which you have to specially MAP in WinUAE) to switch between 1:1 1:2 2:2 modes
I'm using a MUCH later version of WinUAE so I'll try 1.6.0
[Edit: Hmmm cannot seem to get ENTER on the numeric keypad to work on 1.6.0]
BTW: Instead of saying "benchmark x is a big joke" why not recommend something else?