K-3II versus 5D2 is APS-C versus FF. So be aware that on APS-C system, your lenses are cropped, ie focal length is x1.5, and you get a telephoto advantage. Whether that is important to you depends on your type of photography. Those who do for example sports and nature will normally like that advantage. But if you prioritise shallow DOF, maybe FF is for you.
But more than that - with the K-3II (or for that matter, any Pentax body), remember that you can utilise Pentax Limited lenses, both the DA LTD and FA LTD ranges, with their superb image quality and famous, lovely rendering. And they're compact too.
Last edited by KDAFA; 03-08-2016 at 04:53 PM.