I use a GP-Wiz40 in one of my setups & never have had any lag on it. It has been used for a few different Mame builds 147,148,149 & have the 150 build on it now. Play the classics Dk, Pac, BurgerTime, Galaxian, Galaga etc along with the moderns. No lag on it whatsoever & it is a nice interface, would get another in a heart beat.
For 147 & 148, I was using MameUI , MameUIFX
For 149, Mamepui64 & Mameui & then went to Mamep64 cave build using GameEx FE, which is what the 150 is running also. I have used & tried the binaries 149 & 150 of mame w/ GameEx. Never had any lag on the GP-wiz. I have it on Win7 64.
Have you had a chance yet to try it on a different monitor or the crt tv you were saying about?