I jumped from S6PE so I don't know about 8.5
I could probably of stuck with S6PE to be honest, but I liked what I saw when I tried the X1 trial. It sounds like I was lucky because by the time I had got X1 loaded, the X1d patch was out and therefore I didn't really suffer the X1 blues like the early adopters did back then.
For the extra £99 I felt it was a no brainer for me to upgrade to X2 even though I had only just scratched the surface of X1. Automation lanes is what swung it for me, and also the way that you can draw and edit automation data is ten times better than it has ever been in Sonar/Cakewalk.
As others have said though, it's all down to personal choice and it could be that X2 still doesn't do it for you. If you are unsure then I would wait until Cakewalk bring out the trial version.
There are still a few guys here with gripes about colour customisation for instance. And a few have been having issues with downloading files and installing some of the included plug-ins.
If it was me, I would jump straight in, and I did of course, but if you run a pro studio and are worried that it may compromise your work there then I'd hold off. Or, if you can, load X2 onto a separate workstation, if you can. There is one person here who claims that his previous version of Sonar was screwed up when he installed X2.
Good luck with what ever choices you make
andy