iPad 4.3.3 update takes forever, too slow

I'm trying to do this update via iTunes and iTunes says it will take seven hours. Download speed is excruciating. I've tried again and again. Thinking it might be my connection, I did a speedtest and got 18mbps, which I think is reasonably fast. The whole download is something like 600 mb, so should take maybe 10 minutes. I'm using a Macbook Pro, a first gen iPad and Airport Express set up as a "roaming network" to bring the Internet out to my office from an Airport Extreme in the house. Anybody having a similar experience? Any solutions? Many thanks.