To get any insight into this we would need to know the route he was flying. Obviously this is known; whether it will come out prior to the accident report in a year or two's time, is another matter.
My feeling is that aircraft performance was not an issue in this case - other than possibly preventing an IFR flight in VMC on top, due to aircraft operating ceiling limitations.
However, in the latter case, an absolutely key factor is oxygen carriage: did he carry it? If you don't carry o2, then you are chucking away about half of your vertical operating space. You have shut off the most favoured weather escape option even before you departed, and you have excluded yourself from climbing into VMC during much of the year in N Europe. On that (presumed) route, the MOCA is about 9700ft and not having o2 leaves you with no vertical options at all.
Can anybody come up with TAFs/METARs for departure, destination and say Lyon?
MMF - your post crossed with mine and I agree. However, we will never find out what & why the pilot knew & decided, etc. Unless he confided in somebody who stayed on the ground. A vital bit of info would be the radar track & Mode C return.