on a CM and CUC 8.6 install can anyone provide
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Well, you should really start from looking at the v11 Release Notes for both these products to check what extra you are getting and do you really need them or not??
11.x had been there from some time and is quite stable as well but as mentioned above, it really depends on what you are looking to get and is it only achievable with a specific version. If yes, then you will/should definitely go to that version only
Historically .0 releases have a very short span of life until the MR comes out, if they want to upgrade and leave things be for a good time, you might want to think on 10.5, if they want to go to 11.x for some specific new feature no previous version has, they might have to upgrade really soon, when 11.5 comes out.