upr_bench gives following result.

2014/02/03 16:23:34 Recieved 20000 mutations 140926 time lapse per mutation
2014/02/03 16:23:37 Recieved 40000 mutations 139522 time lapse per mutation
2014/02/03 16:23:39 Recieved 60000 mutations 128128 time lapse per mutation
2014/02/03 16:23:41 Recieved 80000 mutations 122561 time lapse per mutation