ePolicy Orchestrator 4.6.8 Release Notes (PD25189)
ePolicy Orchestrator 4.6.8 Known Issues (KB81504)
ePolicy Orchestrator 5.1 Release Notes (PD24806)
ePolicy Orchestrator 5.1 Known Issues (KB79062)
Supported Platforms, Environments and Operating Systems for ePolicy Orchestrator (KB51569)
ePO 5.1 supported products (KB79169)
ePO 4.6 supported products (KB69814)
I can say that 4.6.8 has been quite stable, but then again, for all the beating my head on the desk I do on McAfee products, ePO has never been a stability problem for me.
The most compelling reason to go 5.1 on a new deployment is for getting ePO Real Time goodie compatibility, which is an exciting direction McAfee is headed in. (Got a registry indicator of compromise from your threat intel people? Search every registry in the enterprise in one google like search command...it's pretty slick.)
The most compelling reason to avoid 5.1 is that not all client apps yet are supported on it at least last I checked. That case may not be true any longer. https://kc.mcafee.com/corporate/index?page=content&id=KB79169 lists what client products 5.1 has supported extensions for. For your NDLP, do you manage that standalone, or are you leveraging unified policy with ePO? (I know I sure as heck coudln't get unified to work). If you're managing NDLP from the Manager appliance, epo version is a don't care, looks like HDLP is supported in 5.1. I don't know what DAM is but I think of the word frequently in my McAfee administration. Looks like drive encryption 7.1 is supported.
At any rate, I will say that based on my experience, you can't go wrong with 4.6.8, and that in general, I haven't experienced much if any drama relating to stability with any ePO release I've worked on.
Also make sure your that your ePO version, endpoint products, and client OS version are all compatible.
For example, McAfee Policy Auditor 6.2 is supported on Windows Server 2012, but only from ePO 5.x (https://kc.mcafee.com/resources/sites/MCAFEE/content/live/PRODUCT_DOCUMENTATION/ 24000/PD24694/en_US/pa_620_install_guide_en-us.pdf).
I know that's not one of the products you listed, but just something to think about.