The GROMACS code is now part of the SPEC 2006 benchmark system for CPUs . That means hardware vendors that want to show off their hardware run GROMACS as a part of their benchmarks and some of them tune hardware and/or compilers to get better results. Look for test 435.gromacs to compare your favorites hardware. Note though, that for the benchmark we were not allowed to use assembly code, so the results you see there are in C-code. As a result the numbers are not representative of true GROMACS performance.