[jpstewart]

MIPSPro has features GCC does not. In particular, the -TARG function. You can specify a processor or platform (IP board) to specifically compile against. I'm not 100% clear on platform, and that appears to have a far less prominent effect, but basically:

By default, even if you crank -O3, MIPSPro omits some processor-specific opts. So if I specify TARG:proc=r10000 it will enable R10000 specific features 

GCC does NOT have this flag.

Do you have any info about how -TARG:proc=r10000 in MIPSPro differs from GCC's -march=r10000 option?