Personally, if I was in the market at the moment, I'd find the best deal on the ASUS RT-N16.http://www.newegg.com/Product/Product.a ... 6833320038
Looks like an awesome piece of equipment w/ 128MB/32MB of memory/flash and 533MHz processor (clocked @ 480MHz), wireless N (dual-stream, 300mbps), 3x antennas, 4x Gigabit LAN, 2xUSB (HD/flash/print server), QoS, Download Master support up to 300,000 sessions, the works. And to top it off, if you don't like the stock software, you can install either dd-wrt or tomato (preferably TomatoUSB for the USB support). And since ASUS routers use a special recovery mode for firmware updates means they are very hard to brick. Only real knock is that it doesn’t support dual band, strictly 2.4GHz.
So between the stock firmware, dd-rt, and tomato, you pretty much have every option at your disposal. It was selling for $70 shipped @ Newegg this black friday. That’s the lowest I’ve ever seen. It has been around $80 several times over the past few months.
P.S. I noticed several of your own choices included dual band. Just realize those are SELECTABLE rather than SIMULTANEOUS dual band. IOW, it’s one or the other, not both at the same time. Given the concern for your existing wireless G clients, I’m not sure SELECTABLE fits the bill.
As far as wireless USB adapters, I stay away from them since they have a tendency to overheat (due to the form factor) and that can lead to dropped connections. They don’t necessarily have the best antenna solutions either, a double whammy. Yet, many ppl still choose them and have success. My favorite alternative is a wireless ethernet bridge.
[wireless router]<-- wireless -->[wireless ethernet bridge]<-- wire -->[htpc]
So now you can easily place the bridge for best reception, up to 300ft (w/o a repeater) of Ethernet cable! If it’s a dd-wrt or tomato compatible router in bridge mode, you can even connect multiple devices over the switch. Never any compatibility issues either, works w/ virtually anything that has an Ethernet port. It has others advantages you might not even realize, or at least not until you discover you need them. For example, since it connects to your PC’s LAN port, WOL (Wake On LAN) is supported (wireless USB/PCI adapters don't support WOL)! Definitely costs more, but I never use wireless USB adapters for anything unless forced to, or where it would just be completely impractical to use a bridge (e.g., on the road w/ a laptop).