Hi mendark -)
The most annoying with the A3640 in an A3000 is HEAT! Huge HEAT of the 68040 will cause you multiple boredoms.
Ther is NO space in an A3000 to set up a bigger
disspator and even less for the big fan than would be necessary to keep it cool enough.
You better go for a used cyberstorm as you will get more power than the A3640, Ultra Wide SCSI and a cool 68060.
