Appalling speeds after MAX upgrade

I've just been upgraded from 2 to 8Mbps sync speed, but my actual transfers have plummeted to around 10 to 50 kbps (i.e. dialup speeds). My dad who is on a different exchange was upgraded a few days before me, and he also has an 8Mbps sync speed, but much slower transfer speeds than before (not quite as slow as mine though). Is this all down to network congestion and contention ratios?

How long since the change?

It's fairly common to get very unpredictable speeds for the first few days.

I think its about 10 days now, but I thought it was only the sync speed that changed (and anyway it hasn't, its stayed at 8Mbps), surely the transfer speed should be anything up to the sync speed, subject to contention.

The Sync Speed and Data Rate will change during the 10 day period.

If you get a sync speed of 4mbit for example, it days a few days before the BRAS profile changes to that speed.