The Coldfire is instruction-set compatible with the 68040. This compatibility led to the Elbox company to make an Amiga upgrade daughterboard based on the Motorola Coldfire, running at 278MHz. At this speed it would make for the fastest Amiga ever.
Considering that Workbench can be SMOKING fast, even in high color, on a 25MHz 68030, the Amiga experience on one of these would put almost any PC or UNIX workstation to shame in terms of responsiveness. NetBSD and OpenBSD probably fly on such a box, too. Suffice it to say, I want one ;-)