The boards you are referring to is the MPU, which is where the cpu part of the machine exists. There are essentially 4 different models around. 256MB, 512MB, 1
GB and the latest one that has removable memory and can go up to 2GB. All slot games will work with the 1GB version or better (also runs at 1Ghz speed), almost all will work with the 512MB version (400Mhz speed), certainly the QH titles will run with no issues. It's hard to find anything with the 256MB (300Mhz speed) on an S9000 elite (the one with the widescreen monitor on top). Most mpu's will be of the 512MB variety. The easy way to tell is when the machine boots up, you will see the memory count up. You could also pull out the mpu and get the model number and compare it to this list. It is easy to find these MPU's at the time of this posting, so if you ever run into a game that requires the 1Ghz MPU, you could just buy one, or better yet, but it now and use it and keep the 512MB one as a backup. You are unlikely to source an S9000 with a 1Ghz mpu (unless the dealer replaces it for you), as these were mostly used for V20/20 video cabinets, more specifically Gamemaker HD's. They were later also used on the transmissive S9000 which was short lived because WMS put an end to it with a lawsuit.
PCA39456‐0‐0 this is the 300/400Mhz with 256/512MB fixed memory.
PCA39456‐4‐0 this is the 1Ghz with fixed 1GB Ram.
PCA204934‐0‐0 this is the 1Ghz with expandable memory up to 2GB