You can download FRAPS from http://www.fraps.com, then run the benchmark(F11) during mp. Try to run it on large map with 16 people and dont run it during menu screen etc.
You need to post GPU, CPU, resolution, settings and the benchmark results(just need the ave/min/max fps).
I briefly ran it twice on 16 people deathmatch in Skyline.
Frames: 4598, Time: 46890ms, Ave=98, Min=79, Max=105
Frames: 2887, Time: 29165ms, Ave=98, Min=90, Max=105
Ave=98, Min=79, Max=105 - GTX680(1124/1502), i5 3570K(4GHz), 1920x1080 lowest setting, v-sync on