Well thank you both again for some great insights.
I prefer however to go one more time the Win 10 route before even considering to try 8.1 Pro but at the moment I very curious at just two things that came up in my mind.
These things related to optimal performance and stability
My system will run DDR3 Registered memory sticks I know this, but I have two rated at 1600 mhz en two rated at 1333 mhz - all four of them at 4GB each and all DDR3 Registered. That would put my system to 16 GB of ram while I currently have configuration as I bought it with 4 DDR3 unbuffered single rank 2GB memory sticks and 4 DDR3 unbuffered dual rank 4 GB memory sticks. In total 24 GB.
I read that unbuffered and registered do not go well together, a shame but understandable.
Would it be wise to try to sell off the DDR3 unbuffered 2GB ones for 4 DDR3 4GB dual rank sticks or go fully in with the registered modules ?
One thing I know for sure is that my modules do not do well on the second hand market like they might do in the US or plainly on eBay, but although I have business account on eBay.de (Germany) i find selling hardware items there cumbersome.
Like to hear / read your thoughts on that one.