www.speedtester.bt.com
SNRs good. you are testing via wired ethernet right?
set up a ping monitor, it may be network utilization, high usage.
you could try this >
www.speedguide.net/files/TCPOptimizer.exe < move the marker up top all the way too 100+ then above apply changes at the bottom click on optimal then tick the modify all network adapters box then apply changes > restart > open IE and test speedtest.net