When i did my migration i did it in 1 morning by waves of 20 users. if i remember it's the max (if my memory is good).
regarding move process it took me less than 10 minutes to move 20 Users, now it depend of your link between servers. if it's local network using Giga bytes it should be faster.
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BES 5.0.1 + BES router 5.0.1 in DMZ + BES monitoring 5.0.1 // Server Windows 2008 + Exchange 2007 
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