Same boat here, intermittent web page loading on 2.1 single WAN cox cable here.
I thought it was dns timing out at first, but doesn't matter if we are using dnsmasq, or direct to pubic dns servers.
The clearest way I can describe it from a users perspective, is the browser shows 'connecting' for 10-12 seconds before either loading the page or timing out. It happens once every 10 loads maybe. Switching back to another router solves the problem, but I'd prefer to use pfsense.
I've tried the df bit option, enabling disabling dnsmasq, enabling wan side ping, turning off checksome offloading, I can't figure it out. I'm about to try out monowall and see if the same thing happens.
Hardware wise I'm on: http://www.newegg.com/Product/Product.aspx?Item=N82E16816101364