Vcenter 5.1 to 5.5 on new machine

I have a physical vcenter 5.1 which i am looking to upgrade as well as vitalized. the existing server is 2008 R2 and looking to go to 2012 r2 in the process.  I see there are a couple paths to take and wondering if anyone has hit an issues in this.  My thoughts are either update to 5.5 in place then move the vcenter to the new 2012 r2 VM.  or install 5.1 on the 2012 VM and then upgrade after moving the vcenter instance.  I think the ADAM instance can be an issues when moving between differnt OS versions.