Should I move on to X1 or stay with 8.5

I really like the Pro-channel a lot, and for the price of upgrading that made it worthwhile for me.

All the testimonials in the world aren't going to help you.  You need to find out for yourself how X1 runs on your system, and how it suits your workflow. 
 
Simple as that.  Download the demo.
 

You've got to try the demo at least. There is a learning curve to adjust to it is but well worth making the jump IMHO. As Mully has said the screensets alone are worth it, laid out to suit  they save me loads of time. I have never worked as fast as this and I started on V2.

The jump to X1 requires a big learning curve, which is much more significant than the dollar price of the upgrade (so therefore the "free" demo is still costly). For the amount of time you need to invest, you should be convinced that it will improve your music making experience, not downgrade it.

Right now, the main agreed-upon weakness of X1 is its unreliability, which from a developmental perspective was inevitable given the radical changes in the program and the recession (which means companies can spend less money on testing and feature preservation).

If the forum is to be regarded as a representational sample of Sonar users, then in general, people find X1 to be less reliable than 8.5.3. Of course, some users are lucky and find X1 *more* reliable, but a greater number of people find X1 significantly less reliable, with many reverting to 8.5.3.

If reliability is more important to you than the advertised new functionality, I personally recommend waiting until the next patch (if there is one), or possibly even the next major version (which might be out in a few months).

It'll be cheaper in terms of time and money to wait. And in the meantime, while you continue making music happily in Sonar 8.5.3, you can keep an eye on the forum and X1/X2 videos, to get a sense of whether X1/X2 is "good enough" yet.

Think about it this way: if you upgrade now, your productivity and morale are more likely to experience a net decrease than a net increase. If you're not into gambling, you should wait.

As alluded to you will need to learn X1 so the sooner you get on board the quicker that will happen. It is not your Grampas's Sonar anymore.