Is your serial cable really working?
I recommend you to remove unneeded microcode updates. Check what is your cpu model/cpuid and remove unneded stuff like I did: for example I have modified these files: ./cpu/intel/slot_1/Makefile.inc // leave only your models ./cpu/intel/model_65x/model_65x_init.c //comment microcode includes
this should fit everything to ~80 kB