I've played 3v3 pantheon games without issues, occassionally 4v4. Same thing in custom. I posted details of my router and crash logs in the 'We are here to help!' thread.
I did notice the following in the log each time the custom game starts:
[07-17-2009 11:46:04 646] Ready to try and connect.
[07-17-2009 11:46:04 646] CVPOnPlayerDataUpdatedCallback
You are not authorized to make this request
Not sure if that's significant or not.
I ran the tests on that site too. Things look OK:
http://loki09.mpi-sws.mpg.de//bb/bittorrent-blocking.php?id=1248444920&done=yes&server=74.63.50.30&btport=6882&port2=10010&down=true&up=true&tcp=true&repeat=2&duration=20&peer=174.114.35.56&btup0=104857&btupstate0=6&btupl0=20000&tcpup0=104857&tcpupstate0=6&tcpupl0=20000&btup1=104857&btupstate1=6&btupl1=20000&tcpup1=104857&tcpupstate1=6&tcpupl1=20000&btup2=104857&btupstate2=6&btupl2=20000&tcpup2=209715&tcpupstate2=6&tcpupl2=20000&btup3=104857&btupstate3=6&btupl3=20000&tcpup3=209715&tcpupstate3=6&tcpupl3=20000&btdown0=6606356&btdownstate0=24&btdownl0=20000&tcpdown0=6501493&tcpdownstate0=24&tcpdownl0=20000&btdown1=6544546&btdownstate1=24&btdownl1=20000&tcpdown1=4826466&tcpdownstate1=24&tcpdownl1=20000&btdown2=4887359&btdownstate2=24&btdownl2=20000&tcpdown2=6501493&tcpdownstate2=24&tcpdownl2=20000&btdown3=6501493&btdownstate3=24&btdownl3=20000&tcpdown3=6606356&tcpdownstate3=24&tcpdownl3=20000&&sbtdownl0=21.000&sbtdown0=64913&sbtdownstate0=24&sbtdownr0=0&sbtdownrs0=0&sbtdownp0=6882&stcpdownl0=21.001&stcpdown0=82511&stcpdownstate0=24&stcpdownr0=0&stcpdownrs0=0&stcpdownp0=6882&sbtdownl1=21.000&sbtdown1=73371&sbtdownstate1=24&sbtdownr1=0&sbtdownrs1=0&sbtdownp1=6882&stcpdownl1=21.001&stcpdown1=77484&stcpdownstate1=24&stcpdownr1=0&stcpdownrs1=0&stcpdownp1=6882&sbtdownl2=21.001&sbtdown2=71997&sbtdownstate2=24&sbtdownr2=0&sbtdownrs2=0&sbtdownp2=10010&stcpdownl2=20.024&stcpdown2=209473&stcpdownp2=10010&sbtdownl3=21.001&sbtdown3=77939&sbtdownstate3=24&sbtdownr3=0&sbtdownrs3=0&sbtdownp3=10010&stcpdownl3=21.000&stcpdown3=197934&stcpdownp3=10010&sbtupl0=20.022&sbtup0=6693862&sbtupp0=6882&stcpupl0=20.001&stcpup0=6500989&stcpupp0=6882&sbtupl1=20.001&sbtup1=6605595&sbtupp1=6882&stcpupl1=20.001&stcpup1=4928071&stcpupp1=6882&sbtupl2=20.005&sbtup2=4927038&sbtupp2=10010&stcpupl2=20.016&stcpup2=6591618&stcpupp2=10010&sbtupl3=20.000&sbtup3=6501110&sbtupp3=10010&stcpupl3=20.012&stcpup3=6703614&stcpupp3=10010&
That seconds test doesn't work, it always gives the message:
We are sorry, our tool failed to measure your link (CPE001a92830df6-CM0011e6c43b83.cpe.net.cable.rogers.com - 174.114.35.56): ERROR: No data for upstream