Upgrade ya GFX card and that will make a pretty hefty difference I would guess.
huh? MAME doesn't utilize the graphics card for anything but post processing effects like HLSL.
All the 3D rendering is done by the main processor which is emulating the original hardware.
Concerning BLITZ:
On that particular hardware (vegas driver IIRC), using the 64-bit version of MAME makes a decent difference.
There are DIP switch settings in MAME's in game menu where the original arcade hardware could be set to run at a lower resolution.
Dropping it to the lower resolution helps a bit.
Also make sure HLSL is disabled.
EDIT: There's something weird going on with Mortal Kombat. It should be full speed on both unless you are talking about MK4
DOUBLE EDIT: I'll second paigeoliver's advice on using an older version of MAME. I'm still at 146 on my cab because some games I like won't run at full speed if I use a newer version.