Any advice for poor browsing experience

[#1]

Over the course of the last few months, we've found that very often browsing the web is painfully slow.  Using gmail, or outlook web access, or facebook can be an awful experience of just watching pages load for ages before you can interact with them.  Trying various browsers and multiple devices (two laptops, a Samsung Galaxy S3 and Nexus 7 tablet) all show the same sort of performance.
We use a wireless network as the telephone point in our rented property is upstairs, and all the devices are mainly used downstairs.  The router is a Netgear DGND3700 (fairly new, replaced the last one at tech supports recommendation.)
My last speed test result: http://www.speedtest.net/my-result/3229568103
Router statistics:
ADSL Link                    Downstream            Upstream
Connection Speed 5504 kbps           444 kbps
Line Attenuation         52.0 db                   32.9 db
Noise Margin         2.9 db                        23.2 db
If anyone has any suggestions on anything we could try to improve our broadband experience - I'd be most grateful.

[#2]

Hi, could you please run a speed test using a wireless and a wired connection, for comparison? We need to confirm whether the slowdowns are being caused by the wireless network or if it's a line problem, though looking at the stats you've posted above I'm suspecting the former.