I think the best option would be to use a LAN network speed test....
just googled for it and found this:
http://download.cnet.com/LAN-Speed-Test/3000-2085_4-...
This will give you a good estmate of the speed of your WiFi network based on local conditions rather than knowing it works for 1 person who was sat right next to his router when he tested
Also consider that whilst you might not get 80Mbps via WiFi, think about why did you upgraded?* do you need full speed from a wireless connection, or do you also have an ethernet based PC that can do any downloading that might be required.....
* with sky i'm thinking the main reason to upgrade was the 2Mbps vs 20Mbps upload speed.
Kris
Sky Broadband Unlimited
Ashington (Northumberland) Exchange
Fibre due June 2012!