Needless to say, if you could cool the processor in a Mac Mini (I would probably leave the case disassembled and try to add a better CPU cooler) you'd probably have a better chance of a stable overclock.
After overclock numerous X86 systems, there's one common thread I've noticed. You may be able to get a system to boot at a specific overclock, but the real test is how stable and cool your system is under load (I don't doubt the 1.83 overclock, I doubt its stability under load).
Better cooling definitely helps any overclock and I doubt the (with its compact form factor) that the Mac Mini's CPU cooling is all that great.

[ Edited by Jim on 2010/10/4 0:23 ]