I'm interested in hearing from users who have upgraded from 5.x to 6.x and how long the process took. I am building a copy of our server in a VM to test the process, but without a second server of similar capacity, it's difficult to get an idea of how long the actual upgrade will take. Our install is currently on 5.018NE on Ubuntu 8.04 64 bit, running on a Dell PE2950 dual Quad Xeon with 16Gb RAM and 6 local SAS drives running a RAID10 array. We have 650 users with ~70Gb total mail volume.
I am testing on a Ubuntu 64bit VM, but with only a single CPU and 2Gb RAM. So far, I have been unable to restore the mail from the live server... still working on that part.
If anyone has reports of upgrade times for comparable setups, please let me know. Thanks