Excellent signal, slow connection (same ole, same ole)

I see this problem often, and I have read through some threads to follow advice, but haven't seen any vast improvement.

The basic problem: I get terrible wireless speeds. The signal strength almost always indicates "excellent", however just as often, my speed is listed as 11.0 or 18.0 Mbps.

When I connect to the router with a wire, the speed is great - it's only the wireless that has issues. I've tried two different wireless routers. I've tried two different security settings (WEP and now currently I use WPA Personal). The modem, router, and laptop are all physically within 3 feet of one another.

My specs:

I have a brand new WRT310N v2 Linksys Ultra range plus wireless-n gigabit router. I had a netgear wireless router that gave me the same issues. I purchased the new Linksys wireless router in hopes to fix the issue, but no dice.

I have a cable modem provided by Cablevision's Optimum Online - even pay a few bucks extra for more speed!

My laptop is a Dell Vostro 1500, running Windows XP SP3

As best as I can tell, my laptop's wireless card is a Dell Wireless 1390 WLAN Mini-Card.

my internet connection type is: automatic configuration DHCP

My network mode is mixed
I've tried channel 1, auto, and now use 11
My channel width is 20MHz only

other than insanity, that's all i got

any ideas?

I don't think 11 or 18mbps is bad for wireless, given that it's a duplex system and always ends up at around half the speed of the equivalent wired system.

Try not using mixed mode.

Bear in mind that an "excellent" signal doesn't actually mean anything -- quality is the other half of the equation.

So try raising the router above furniture level, experiment with different channels (because different ones work better in various environments -- it's a physics thing). If detecting neighbouring wifi, try a channel 5 stops from the strongest.
Relocate cordless phone base or video sender away from the computer or router.