I can't reach that value with a Dell OptiPlex GX280 w/ onboard bge(4) MP kernel, net.inet.ip.ifq.maxlen=250, 4.0 or -current, doesn't matter. Collision count increases monotonically. Stops forwarding packets, etc. Switching to em(4) carries limit to ~25k to ~30k.
consider trying to increase ifq.maxlen higher than that and see if it helps. It did for me.
--Matt
