You don't say what model i5 you have.
2.7Ghz i5 or 3.5Ghz i5?
prescale on HLSL has been the culprit on my setup (which is still on v.146 and has an old 3.4Ghz Athlon X3)
I had to reduce the prescale on old games that had discrete sound emulated and turn it all the way down on 3D games.
If you're on the newest version of MAME, rolling back to the 150's might help.
Running a second monitor does tax the system more.
I can run Ridge Racer full speed in MAME on my 3.4Ghz i7 laptop, but get stuttering if I try to run both the laptop screen and living room screen at the same time.
One or the other and it's fine.
Just FYI, Howard (author of mamehooker) usually sticks to the software, console, & everything else forums so post in the software forum if you want his input.