I had exactly the same problem (funnily enough in CS:S!) when my line went from 512K up to 2Mb.
I tried all sorts of stuff - dumped the QoS driver, fiddle with the MTU, other technical stuff - but it just carried on. General surfing was ok, but maxing it out when gaming just sucked.
In the end I went out and bought a new Linksys modem/router ... that fixed the problem! Turned out that the Netgear wasn't designed to work with anything more than 1/2 Mb, so it couldn't handle the higher rate.
Check the specs on your adsl box as you might have the same problem.
PS: Come and have a go at 83.142.52.155:28015 if you fancy a good pasting
