As the deadline of the project is arriving at a very high speed I need to choose a chip that has good documentation and free tools like compilers and emulators.
running SILabs chips using SDCC shold fulfil that.

I thought I could say that ATMega128 has twice the the program capacity of a 8051. This is very important to understand this: could you point me to information about this?
comparing the ATMega128 to the 8051f120
Both have 128k of flash and both have a 16 bit address, thus both must use some kind of paging scheme if you use more than 64k of program space (which, in my opinion, is ridiculous on an 8 bitter). The 8051f120 is more "peripheral rich" and has 8k +256 bytes of internal RAM, where the ATMega128 has only 4k

Do you mean that a peace[sic] of software that as a memory footprint of 30KB on ATMega128 has a 15 kb on 8051? I am confused
sure, so would I be hearing that, my GUESS would be that some apps would be smaller on one, some smaller on the other.

I have to purchaise an external SRAM ship to feed ATMega128 because communication stack consumes lots of RAM. if 8k is not enough, you must do the same for the '120


What about the NMIY-0031 board?
never heard about it, link, please

Erik