Earwax
I use Sonar mostly as a digital tape recorder. No one has convinced me that X3 (or Artist, Professional, or Platinum for that matter) actually SOUND better than 8.5.3.
Actually IIRC it was Noel that said at the base level no DAW will ever sound better than any other DAW. Digital audio is digital audio and would sound the pretty much the same unless the developer chose to add "something" to the base DAW (pretty much like the users of Harrison MixBus believe, and no let's not get into that here).
What has happened (as I'm sure you're aware) is that the X series (including the New SONAR) has had enhancements that some cannot live without and others welcome with open arms. There is no point in me telling you what I like as it's not germane to you and what you do with your DAW.
Heck I know some active posters here who still use a version of SONAR older than yours and are perfectly happy and they produce excellent mixes to boot.
Glad it's working for you.