In reply to a post by adebov:

Maybe give it a few days.
I had exactly the same thing when I switched from 40/10 to 80/20. Download speeds on everything (except multi-thread downloads & Usenet) were below 16Mbps.
It was so bad it appeared (and I'm still not sure it wasn't) BT were throttling each download thread.

It seemed to recover 4-5 days after the upgrade.