I used to have a BEFSR41 v2 but have moved on from that 5 year old design.
AFAIK the v1 and v2 only had a half duplex 10 Mbps WAN port.
I've seen reports that they can't handle 6Mbps but earlier versions of firmware such as V1.39 could.
see
http://www.dslreports.com/forum/rema...on+firmware+46
for example.
But doesn't explain why it should crash the cable modem unless the duplex mode is not been set correctly?