ID tag (98640014) is model specific, more having to do with the way Mitsubishi handles its shops turn-around time in manufacturing/servicing and the protocol they decide to build their engine/transmission setups on. I know someone posted this in one of the first posts. At any rate, 98640014 is your car.
The “evo7base” is the file that contains “scalings”, or the mathematics that directly relates the data on your ECU to you (and then back to the ECU). The reason it is the same for the EVO 8 is that there were probably running the same basic engine management set-up, just manipulating the data in the later years for “pollution control” reasons and data upgrades. The 98640014.xml is used to define the ECU data, along with the help of the evo7base scalings, to adjust the stock map.
I am sure there are other ROMs, based on modifications, which may work for gaining performance, although there should be a nice pile of research behind this. For instance, I would research on the engine/transmission of the ROM being used right down to the pin-outs to the ECU.
Modifications of this nature are posted on sites like:
http://forums.evolutionm.net/forumdisplay.php?f=179
http://www.osecuroms.org/
Both outstanding sites. Good luck!