Just wanted to post back with an update. I picked up the RT-N66U, and it definitely made a significant difference performance-wise. Generally about 10mbps faster and I could definitely tell the difference in Crysis 3 MP. My connection is 50mbps. With my wrt54GL, speedtest.net would generally average around 42-45mbps. With the RT-N66U, I average about 53-56mbps. Not bad.
However, this is one finicky router. Almost impossible to brick, it would seem, but definitely unusual.
Initially, I flashed Shibby Tomato. It took 2 days. The first day, I flashed several times between factory and Tomato and just could not get it to come up again. Most of this was using the Firmware Restoration utility. The 2nd day, I flashed again to tomato and let it sit overnight (as suggested in many posts around the internet). Finally, Tomato came up. But I wasn't too impressed and couldn't get the vlans working (although configured properly). I also tried to flash dd-wrt, but no go.
I liked the Asus fw and interface, so I flashed the latest, then flashed Merlin and stayed there. I accomplished my isolated subnets with additional routers instead of vlans and it works fine.
Now, however, after a week of running fine, it won't stay connected. So I've RMA'ed it to Amazon. It's also a pain to reset if power fails, etc. Unplug everything, plug back in, get into setup, setup tells you to unplug the modem again, then plug it back in, it finds the modem, connects, then runs through a few setup items (including verifying settings for wireless), then reboot PCs. A 10 minute process. My wrt's only require power cycling the modem to work again.
My replacement will arrive Mon., but it's definitely been an experience with nice performance gains to compensate. Just wanted to convey my appreciation for the advice and share my experience. Thanks!