Yep, Picasso96 makes a massive difference in WinUAE, since a lot less work is required of the host PC when the native graphics chips aren't used. I would check as well that you have the Fastest Possible speed set, as using the cycle-exact timing will cause the emulated CPU to wait for the emulated chipset. Some games will need this setting, but for Workbench use it's far better to use as little chipset emulation as possible...
