Apoligies if listed elsewhere as seems a basic question.

I have just bought Belkin Play Max (N Dual Band 900) router.
My broadband provider can get me 8.5mbs
When connected via Ethernet I achieve 6.5mbs+.
When connected via wifi I achieve between 0.5 and 2mbs.

I can be stood next to the router with full wireless signal.

I run laptops, ipads, pc and smart phones off wireless and will be adding apple tv.

The router is off the ground in a central location, plugged into master telephone switch and not near our cordless phone (although we do have Panasonic DECT phone running through house I did unplug this and no change!)

I have a Sonos ethernet connected to rear to create a seperate wifi mesh network for streaming music throughout the house. There are about 8 other devices that receive and retransmit this around the house. This broadcasts on channel 1. I have tried unplugging this but it makes no difference.

I was set to Auto Channel on 20/40 but have tried changing this to channel 11 and 20 mhz.
I have also tried changing to the 5ghz option instead of 2.4ghz but this makes no difference.

InSSIDer 2.0 shows one other new wireless signal within range at my neighbours house.
They have just moved in and are using Channel 11 on their Cisco router.

All Belkin have told me to do is move to Channel 11!

What else can I do to get closer to the actual hard wired speed available?

Aplogies for what seems a basic question but I am struggling...

Thanks