Modem opinions

I brought my brothers computer into my room and hooked it up on my phone line and i connected at 50.6 bps, my comp only connects at 49.333 max and thats only if i am lucky. We have the same system for the most part. The only real difference is we have different mother boards, i have a athlon 2200+ and he has a 2000+, different video cards also. The main difference is he has an internal zoom modem and i have an external usb zoom modem. He runs XP but i used to run it and i never connected as fast as his comp does on my phone line. I am wondering if his internal modem is whats giving him the faster connection speed or if it is something else. We're both running the latest drivers.