How about making M0n0wall 1.3b (or start a new branch) based on FreeBSD 7?
At the moment the beta is slower than the stable 4.x based version, as a matter of fact. So I do really hope Freebsd 7.0 core will be considered for the final 1.3 m0n0wall release because network speed in 7.0 is way better than 6.x, then you have also better hardware support for a lot of USB network cards based on the new "axe" chipsets.