Here are my benchmark results for different compilers - using the dhrystone 2.1 benchnmark from aminet (more benchmarks may follow):
1. gcc-4.0.4 -O3 -fomit-frame-pointer -m68000
2. gcc-2.9.3 -O3 -fomit-frame-pointer -m68000
3. vbcc-0.8j -O=65535
4. sas/c 6.58 opt optgo nostkchk
5. gcc-4.0.4 -Os -fomit-frame-pointer -m68000
6. gcc-2.9.3 -Os -fomit-frame-pointer -m68000
7. vbcc-0.9e -O=65535
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EDIT: "gcc-3.4.6 -O3 -fomit-frame-pointer -m68000" is on par with gcc-2.9.3!