MAME underwent some major changes after version 0.116. I build many varying-spec PC's and found a similar problem. Although my initial upgrade to XP revealed some slowdown, this was soon remedied on any version of MAME by doing some XP tweaking (removing messenger and some other services or installing TinyXP).
The problem still exists however with the major graphics re-write in 0.116. The MAME dev team basically conceded and started writing the graphics drivers around modern hardware, thereby making new releases slow down or fail to work on older machines, but excelling on newer machines.
Cut short, if running a P3 or older with low-end graphics cards, stick with pre-0.116 MAME. If running a newer pc with better graphics hardware, go for MAME 0.116+.