As an interesting asside to a couple of points. I had need to look at some cores some time ago. Not specifically at 68k but from what I recall many of the cores currently implemented have been purely described in something like vhdl and then 'optimized' for speed etc. After looking around a bit however you can actually find a few cores where people sat down with a bag of logic and breadboarded it. In terms of gate count there are some clear size differences, which led me to question some of the 'optimizations' going on between cores of the same type.
As far as the 68k goes, motorola themselves have a 'softcore' program and several other firms have it for sale as a core. These people have already done this and know whats available. There is also a 68k vhdl skeleton floating around somewheres for free. If I were interested in this first port of call might be motorola themselves?
RE: Atari ColdFire Project