Here are some files from a pre-1999 Audi S8 (4.2 32V, 340 bhp). The ECU uses an Intel MCS-96 microcontroller and 2x64 KB ROM through bank switching.
The first file is stock. The second has the 250 km/h speed limiter removed, and the third has tuned maps and the usual speed limit.

http://leitseite.net/misc/ecu/s8_stock.bin
http://leitseite.net/misc/ecu/s8_no_speed_limit.bin
http://leitseite.net/misc/ecu/s8_tuned.bin

I compared these files, and found the following changes from the first to the second file.

0x8442 - 6 bytes changed to FF. Doesn't seem to be instructions (and 0xFF is RST on this CPU, not NOP)
0x87C4 - 67 00 changed to 00 FF
0xB239 - map with slightly raised values
0xB57A - same as above
0xBF00 and 0xBF03 - probably the checksums for ROM bank 0

I wonder if this ECU really has a VMAX setting or if the limit was implemented through some other method. Is this possible? Does anyone know more?