I have both Verizon fios and Comcast cable internet to my house for the reason that both are unreliable in different ways. I have been manually switching to Comcast when fios goes on the fritz, but I ...

and simply switch between the two providers by changing the default gateway of the clients betwen .1 and .2? Each ISP's firewall would be nat'ing the same subnet: ISP1 firewall (Cisco Pix): nat ...