i dont really wanna get into specific specs here...but here's how i look at it...
it depends on what simulation youre actually doing.
intel cores are better for multimedia stuff...games and stuff. this is mostly because theyre built with a faster front side bus. the processor communicates with hardware faster, but the core is actuallay slower than an amd.
amd cores are actually better numerical processors. theyre designed with a slower front side bus, but the core is actually better capable of crunching numbers.
the mhz rating will be the same because this is figured by multiply the frontside bus speed with the actual core speed.
also, look for more higher end processors...something with larger built in cache (level 2 cache and stuff)...especially when a single dual-core processor has a separate cache for each core. this will give you a higher overhead for data waiting to be processed (your system wont lag or jerk when the processing load jumps suddenly)...
of course, you cant go wrong with multiple processors either.
hope this helps, you asked a pretty tough question here. its hard to answer this in just a few lines.