Shan, I'm in the same boat as you. I thought a 3-day downtime was a bit excessive for an upgrade, but such is the Aspect Software process. I lived through a 20 hour upgrade this year and that was just for a minor Code Mod to 6.5.1..
One technique (that is expensive) is to rack new servers for the new version instance and let Aspect install it while you run on the old instance. We are actually doing this at one of our centers b/c it will allow a quicker rollout/rollback strategy. The other Aspect instance we have has too many servers to make this financially feasible. We have a backup, auxiliary ACD (separate, non-Aspect ACD system) that we intend to use during that upgrade.
Please make sure the folks supporting your servers have an adequate backup in place in case something must be restored. That stipulation is in small print in the customer requirements..
Good luck!