Upgrading ZCM 11 to ZCM 11 sp2

Been doin a lotta readin about upgradin zcm 11 to zcm 11 to sp2...

I was just wondering if there are other options from a straight up upgrade...

current env :
VM(esx4.x) machine : win2k03 r2 sp1
c: OS
D: ZCM repository

database SQL 2008

i know snapshots is a good and reliable failsafe for "just in case scenarios"...but

what i was a thinkin :

create a new vm under our new esx5 env
OS : Win2k08 R2 ( patched to the high heavens )
C: OS
D: zcm partition( easier to increase space just in case )

Install ZCM 11 sp2 ; as a second primary server( with its own local database? )
scrap old ZCM server

concerns :
since the upgrade requires shutting off the ZCM services during the upgrade process; what happens to existing clients?
I believe this is less risky and would incur less downtime...

please advise...

thanks,
Kahlil