I always just buy sockets and oscillators from DigiKey, or swipe oscillators out of other junked equipment. 
I bet that a 33MHz 68040, a nice heatsink (think fast 486 or pentium HSF), good thermal compound, and the right crystal would be all you'd need for 40MHz. Beyond 40MHz your mileage may vary with a 33MHz chip. Some have reported 45+ on 33MHz rated chips, whereas I couldn't get my Turbo040 stable at 48 until I bought a real 40MHz chip.
I think it would be awesome to use Rockets to do the kind of MP things that old Macs actually did back in the day. Network-rendered AfterEffects all inside one box comes to mind. Another idea would be for maximum Mathematica 68k performance: run the kernel on the Rocket and the frontend on the motherboard Mac.
I bet that a 33MHz 68040, a nice heatsink (think fast 486 or pentium HSF), good thermal compound, and the right crystal would be all you'd need for 40MHz. Beyond 40MHz your mileage may vary with a 33MHz chip. Some have reported 45+ on 33MHz rated chips, whereas I couldn't get my Turbo040 stable at 48 until I bought a real 40MHz chip.
I think it would be awesome to use Rockets to do the kind of MP things that old Macs actually did back in the day. Network-rendered AfterEffects all inside one box comes to mind. Another idea would be for maximum Mathematica 68k performance: run the kernel on the Rocket and the frontend on the motherboard Mac.