MAME game runs worse through Attract Mode

[AchillesPDX]

Pulling my hair out here as I have no idea what's wrong or how to fix it.

First, my setup:
AMD Phenom II X6 1090T (Stock)
AMD Radeon 6870
8GB RAM
Windows 10 Pro 64-bit
Mame0173b_64bit (HiScore, No-Nag, DirectInput)

My problem:
Launching Run And Gun 2 directly from within MAME with HLSL enabled runs beautifully - zero frameskip nets me a rock-solid 100% speed with vsync enabled, and in fast-forward mode it hits like 160% during gameplay.
Launching Run And Gun 2 from within Attract Mode using the same exact version of Mame and settings nets me a garbage 68% speed during gameplay.

Anyone have any idea what the hell is going on and how to fix it? I need to check some of the other games that have been giving me slowdown problems with Attract Mode and test launching them straight from Mame, but this has me concerned - could Attract Mode really be using up that much horsepower while running in the background?

Thanks in advance peeps.

[AchillesPDX]

Well, after a bit more fiddling, it's not Attract Mode causing the problem - it's running Run And Gun 2 from the command line that causes it. Off to mamedev.org!