Been away from Cakewalk for a bit. The skylight interface in X1 didn't agree with me, so I tried another DAW for a while. But I missed some things about Cakewalk so I'm back and considering the upgrade to Sonar Artist. Artist is all I need because I have plenty of quality 3rd party plug-ins, etc.
 
A couple of questions: Will the new sonar open projects created in Guitar Tracks Pro3?
                                What does Artist have going on that makes it an improvement over X1?

Don't know about Guitar Tracks Pro3, but Sonar 2015, for want of a better name, has a lot of bug fixes and incremental changes compared to X1. There's a whole bunch of stuff in all versions X1 either didn't have as well.
 
You might find it worth considering Professional as well as artist, the pro-channel has some very nice stuff in it. There's a comparison of the various versions here http://www.cakewalk.com/Products/SONAR/Versions

Thanks for the reply. I will ask the GTP3 question in a new thread. I think it will be overlooked here.

I still have .wrk files from GTP that open fine in SONAR 2015. Missing plugins are about all you will see pulling those into SONAR 2015 (same as if you open them in X1).

A lot of process improvements have occurred since X1, including VST3 support, Speed Comping, and several others.

Thanks mettelus!