Upgrade Vsphere 3.5 to Vsphere 5.1

Hi all

we have 5 Vsphere 3.5 Esx servers with a vCenter server 3.5 in  (HP EVA storage)shared storage.

we are plaining to upgrade this in Vsphere 5.1 in EMC VNX5300 (Block Level) shared storage.

Our Old ESX servers are running in HP Blade server but our New server will be in Dell M620 Blades servers

My question is

• can we first upgrade vsphere 4 and then migrate to Vsphere 5.1 but its a very long process
• or first we connect new storage with old storage switch and then migrate & the old  VMs to new storage
• Or can we prepare a new setup in Vsphere 5.1 & then move the storage Data

or if somebody has any other method then pls let me know . Thanks in advance..