whatzcrackn if you already have the P4 3.2 go with it, It will run most things in mame, you may want to get a cheap graphics card though Radeon 9600 pro of something like that.
I'm sorry but I'm going to high jack your thread, but hopefully you and everyone else here will find this info useful. I'm on holiday just kicking around the house because I can and as I work in IT sales I have access to no less than nine PC in the house, so to put the performance debate to rest I spent the better part of 8 hours today benchmarking a group of performance hungry M.A.M.E. Roms.
All system were benched with the same copy of M.A.M.E. 0.118u4 & matching ROMs. all roms were decompressed.
I used the following command line in a batch file:
mame.exe -noautoframeskip -frameskip 0 -seconds_to_run 240 -nothrottle -nosleep -video ddraw -skip_gameinfo -effect none -nowaitvsync -noreadconfig %1 (where %1 is the name of the ROMSET)
I used 240 second instead of the normal 100 for the duration as the start up test screens tended to distort the results, the larger test time countered this effect and gives truer results in my mind.
PC one:
Intel Core 2 Duo E6420 (2.13ghz stock) from here on in referred to as "C2D"
Gigabyte GA-P35-DS4 Motherboard
2x Corsair 1gb DDR2-800 Dimms
Geforce 8800 GTS 320mb graphics card
Windows XP Pro standard install.
PC two:
Intel Pentium 4 socket-478 C-Series (3.0ghz stock) from here on in referred to as "P4C"
ASUS P4P800-SE motherboard
2x Corsair 256mb DDR-400 Dimms
2x Corsair 512mb DDR-500 Dimms (when pc overclocked)
Radeon X800 XT 256mb graphics card
TinyXP stripped to the bone.
PC three:
AMD Athlon64 X2 4200+ 939 (2.2Ghz stock) from here on in referred to as "AX2"
Gigabyte K8N-SLI motherboard
2x Corsair 512mb DDR-500 Dimms
Geforce 8800 GTS 640mb grahpics card
Windows XP Pro (optimized)
I selected a group of ROMs with low benchmarking results from Mame Benchmarks and tried to get a good spread of game types.
Results:
BLITZ (57hz)
C2D (2.13ghz) 56.70%, 32.32fps
C2D (3.20ghz) 84.53%, 48.18fps
C2D (3.60ghz) 94.44%, 53.84fps
P4C (3.00ghz) 37.23%, 21.22fps
P4C (3.50ghz) 43.44%, 24.76fps
AX2 (2.20ghz) 45.28%, 25.81fps
(get a Core 2 Duo to 3.8Ghz and your home free on this one)
CARNEVIL (57hz)
C2D (2.13ghz) 134.05%, 76.41fps
C2D (3.20ghz) 197.96%, 112.84fps
C2D (3.60ghz) 222.20%, 126.654fps
P4C (3.00ghz) 85.16%, 48.54fps
P4C (3.50ghz) 100.33%, 57.19fps
AX2 (2.20ghz) 93.27%, 55.44fps
CALSPEED (57hz)
C2D (2.13ghz) 39.47%, 22.50fps
C2D (3.20ghz) 63.97%, 36.47fps
C2D (3.60ghz) 65.30%, 37.60fps
P4C (3.00ghz) 26.23%, 12.10fps
P4C (3.50ghz) 29.84%, 17.01fps
AX2 (2.20ghz) 31.90%, 21.60fps
(looks playable but the number don't back it up not sure why)
CRUSNUSA (57.35hz)
C2D (2.13ghz) 121.17%, 69.49fps
C2D (3.20ghz) 183.57%, 105.28fps
C2D (3.60ghz) 205.83%, 118.04fps
P4C (3.00ghz) 85.32%, 48.93fps
P4C (3.50ghz) 99.59%, 57.10fps
AX2 (2.20ghz) 83.48%, 47.88fps
GAUNTLEG (57hz)
C2D (2.13ghz) 34.65%, 19.75fps
C2D (3.20ghz) 32.50%, 18.53fps
C2D (3.60ghz) 36.47%, 20.79fps
P4C (3.00ghz) 26.56%, 15.14fps
P4C (3.50ghz) BSOD (quick and dirty overclocking doesn't always play ball)

AX2 (2.20ghz) 29.34%, 16.72fps
(The Gauntleg doesn't really scale, I would expect this to change and there to be a jump in performance in a future version of M.A.M.E. )
MACE: (57hz)
C2D (2.13ghz) 63.01%, 35.92fps
C2D (3.20ghz) 90.04%, 51.32fps
C2D (3.60ghz) 100.53%, 57.30fps
P4C (3.00ghz) 40.70%, 23.20fps
P4C (3.50ghz) 45.07%, 26.049fps
AX2 (2.20ghz) 49.53%, 28.23fps
PROPCYCL (60hz)
C2D (2.13ghz) 37.01%, 22.21fps
C2D (3.20ghz) 55.14%, 33.08fps
C2D (3.60ghz) 61.95%, 37.17fps
P4C (3.00ghz) 24.51%, 14.71fps
P4C (3.50ghz) 27.68%, 16.61fps
AX2 (2.20ghz) 28.79%, 17.27fps
(Propcycl pauses on the first couple of balloons and I think this hurts it's score, it looks playable a 3.6ghz on the Core 2 Duo)
XEVI3DG (60hz)
C2D (2.13ghz) 156.25%, 93.75fps
C2D (3.20ghz) 233.98%, 140.39fps
C2D (3.60ghz) 262.49%, 157.49fps
P4C (3.00ghz) 115.28%, 69.17fps
P4C (3.50ghz) 133.48%, 80.09fps
AX2 (2.20ghz) 90.17%, 54.10fps
(XEVI3DG seam to like the P4 better than the AthlonX2, go figure)
If you look at the numbers carefully you will note the performance goes up at the same rate as clock speed, the P4 at 3.5ghz is 1.2x its original speed, and it's scores are 1.2x those of the process at stock speed, the same is true of the Core 2 Duo it's scores at 3.2ghz are 1.5x those of stock and at 3.6ghz 1.69 times those of stock.
Useing this as a guide you would need a Pentium 4 at 4.5ghz to match the scores of a Core 2 Duo at 2.13ghz. So you don't need 9ghz CPU to run CHD games you just need the right processor, which currently is an overclocked Core 2 Duo. (oh and before anyone asks a socket 775 prescott P4 is no better, it fact a 2.8ghz P4c at 3.5ghz 1000fsb will beat the hell out of a 3.6ghz Prescott at 800fsb even with DDR2.)
So if your shopping for the ultimate M.A.M.E. rig, get a Core 2 Duo E6850 overclock it to 4ghz and game away, I just so happens to be waiting on the last part for my 4ghz C2D setup to come, so I'll probably post score for it in about two weeks.
Anyway, if anyone has any questions about all this hit me with it.