What's your target machine? A1200 or A3000/4000? And what's your basic usage? I personally find that when primarily using Workbench and related applications are a little faster on a 060 than a good 040, but that it is not a huge difference.
For example a WarpEngine with 40MHz 68040 also provides a good SCSI controller. There definitely is a noticeable difference with the Phase5 Cyberstorm Mk2 when doing CPU intensive things (such making a LHA archive of your complete drive) but it's not stellar. Now given the price difference and availability I'd go for the WE...
