but I thought I read somewhere to try to stay below 8ms response time for Mame...
Don't bother response time. It's (almost) useless information. A little bit of trailing on an LCD looks at CRT ghosting in the worst case, but does not affect gameplay. Lag affects precise timing in say Donkey Kong
From fastest to slowest (there are exceptions off course):
-OLD TN panels (with 18bit colour and dithering): <5ms lag
-IPS panels: 8-16ms lag
-MVA panels: 8-16ms lag
-NEW big TN panels (>22 inch with PWM 24 bit colour simulation): 16-30ms lag
-IPS panels with extensive hardware calibration: 30ms lag
-PVA panels with overdrive: 30-45ms lag
-PVA panels with overdrive and extensive hardware calibration: 30-60ms lag
16ms is 1 frame delay, and is completely acceptable as maximum delay for serious gaming.
So regarding the Dell 2007PF:
If the serial ends with an L, its an IPS screen, and its OK, ending with an S means SPVA. That's better blacks, but more lag
The HP had similar things. It's delivered as IPS and as MVA display, but as you can see, MVA is on par with IPS for speed.