That's not beefy enough TIM. Even my setup runs it a bit slower.
Results without graphics, just CPU computation for MK4 is this: Average speed: 66.65% (89 seconds)
Processor Name: Quad-Core Intel Xeon
Processor Speed: 2.8 GHz
Number Of Processors: 2
Total Number Of Cores: 8
L2 Cache (per processor): 12 MB
Memory: 6 GB
Bus Speed: 1.6 GHz
Also your 64bit OS is not going to net you a huge benefit other than allowing you to access more RAM, it doesn't process any faster so don't list it as a "beefy" trait. More RAM wont help you here either, the game is rather small.
With emulation the processor that is the biggest lag, these games aren't very advanced graphically but do duplicate the work of all the processors since it's emulated. So little is known about the hardware the MAME team can't really think about optimizing it yet until they know more. Until then, building a bigger system will only marginally help. It'll be cheaper to buy the arcade game.