Mine took about 80 minutes. I think that it has more to do with server load than internet speed, (I have 10 Mb/s). 380 MB should have only taken about 10 minutes.
50Mb download here took under 4 mins.. It will be down to your distance to server..actual connection speed (may also be down to your network configuration, wireless etc.).. and the server busyness!
I think my update was around two hours. It initially said like 128 minutes but I played some Mass Effect 2 on my 360 while it was downloading, so I never got to precisely time it.
Probably the PD has a NLB system (Network Load Balance) on their servers that is not working very well.
Here is what everyone can do, worked for me, whenever you enter the game the online game update takes you to one of PD's servers, so when you leave (cancel the update) and start the game again, you probably will fall on another download server.
So keep trying to enter and cancel the update until you find a connection that is best for you area or a server less loaded.
It was happening to me, 500 minutes for the download! Until I find a server that downloaded the update in 20 minutes (it took me 4 attempts).