Thank you for taking the time to answer. It is so difficult to take a decision. Another thing I noticed in the P6 forum is that there are many messages related to issues or problems with some aspects of the P6. Not sure if this is because it has many more users than the OB or it is only a perception I had. How do they compare in terms of materials and crafting? Have you had issues with any of them?
I have the keyboard version of the P6 and the desktop OB-X8 (both bought new), and have not had any much issue with either of them, I would not say comparative reliability is a factor in my case. The P6 does have some play in the knobs (look up wobbly knobs, known issue on a lot of Sequential synths) which is a little annoying if you overthink it, yet I've never heard of any reports of these coming off or breaking or suffering anything beyond the annoyance - the OB knobs feel more solidly placed.
I qualified that with "bought new" because I sometimes see different experiences from folks that bought used, which makes me wonder about the history of the hardware or if it was sold for a reason.
I have heard some describe the tone of the P6 using terms like "harsh" which made me wonder if there were some issues with their particular unit, as its not a characteristic I would associate with this synth. And I have heard others say that they heard two different P6's and they were very different, which makes me wonder if there was a bad manufacturing run at some point.
As far as more issues reported for the P6, it's been out a lot longer in total years. It also came out at a time when not many pure analog polys were available in the competitive range, so it doesn't surprise me if it has more hands on it (which will always lead to a higher quantity of negative feedback).
Other differentiating factors to consider, the P6 is one of the more "immediate" analog polys available.. hard to describe but everything just does what you want it to without thinking. The OB is a little more menu divey, but rewards on sound.