Advice Needed: How to Migrate VM from 5.0 to 5.5

Existing Setup

1 X vCenter 5.0 (running SQL 2008 R2 on itself) and managing 2 different clusters:

Cluster A: 2 X ESXi 4.1 hosts, 3 X datastore on vmfs 3

Cluster B: 4 X ESXi 5.0 hosts, 7 X datastore on vmfs 5

Targeted Setup

- Setting up 1 new vCenter 5.5 U1 (pointing to a new SQL)

- Adding 2 new ESXi hosts to each cluster (total 4 new hosts)

At the same time:

1. I am trying to upgrade all the ESXi hosts to ver 5.5 & join to the new vCenter 5.5.

2. After setting up a new vCenter 5.5 U1, we will decomm the old vCenter 5.0.

3. In addition, I would like to upgrade all datastores to vmfs 5 as well.

Question

As there are production VMs running, is there a way to perform the migration with least downtime?

(All the existing datastores will be presented to the new ESXi hosts)

Thanks in advance!

Rayretro