Having just moved from an iPad3 to an Air and my wife is using an IPad2 I have been able to compare all three. The iPad Air loads pages much quicker than the iPad2 or 3 under normal circumstances.
I am also with BT with an average download speed of 9 to 10 Mbps, there are times in the evenings when page loading is slower however streaming video from iPlayer, for example, still works fine. The bandwidth, especially on copper lines, has limitations. Isp's have to manage the amount of traffic on the lines especially at peak times. More and more people are streaming TV and video over the Internet so much more bandwidth is being used now than a year or two ago. In order to allow stable streaming iSP's will limit some traffic over their system and general web browsing is probably one of them.
We have a desktop and two laptops In the house too and they are no quicker than the iPads at loading web pages. As has already been stated, depending on what you do, the iPad is not a complete replacement for a computer.
In my opinion the iPad Air is currently the best tablet available on the market and in your situation I doubt very much that it is the cause of the problems you seem to be having.