Lets look at what the OP is using. He is currently using a rented Comcast modem. Their top of the line X1 router/modem combo (TG852G, TG862G, SMCD3GNV, TC8305C) uses G and N or A (2.4ghz and 5.0ghz) and is set up with a default to G. 2.4ghz. In perfect conditions, it is capable of 54Mbps, but we both know that is never achievable. Even next to his router, with 0 interference and other devices using the same channel, he would be pretty damn lucky to get 45mbps. He claims that he gets 28-32Mbps, and my best guess is the router has a wall or 2 to get through to connect to his devices.
The N or A both have much higher throughput, but their penetration is greatly less than G. OP might even encounter slower speeds on the 5ghz spectrum because of the distance between his router and his connected devices. Generally I only recommend 5ghz for people who live in dense areas like apartments where the 2.4ghz channel spectrum is saturated because once you break that line of optimal distance from the router, your speeds drop off quite a bit due to signal strength degradation.
But this entire argument goes back to my 1 simple request to test the speeds plugged directly into the modem instead of through wifi.