5) Speed: The WRT54G maxed out ~20Mbit (wired) and 6-12Mbit (wireless) running Tomato. The RT-N66U does around 50/225Mbit wireless/wired and the RT-AC68U pushes 400/900.
I get around 42Mbit routed throughput wired, with firewall enabled, QOS disabled running dd-wrt on a wrt54gl. Far more than your 20mbit, but still i think this is the keypoint where this device has aged too much.
If you are good, you will be assigned all the work. If you are real good, you will get out of it.