Already have X3e Pro.
What would I "be missing" if I just used the new Artist version?
 
I already have the paid full versions of Rapture, DimPro, z3ta+, Pentagon, and Melodyne.
Also have the Arturia V-Collection that I use a lot.
So, I can't see any need for some of the new synths or effects.
But... would the effects that I already have as part of X3e and the older 7PE work in "artist"?

Oh, and I haven't used the pro channel stuff at all in X3e.
 
Thoughts please.

Artist version does not support Pro Chanel and since you don't use it you may not "miss it".
 
I'd contact support to see if any specifics would be lost if you went Artist.
 
Safest route probably would be SONAR Pro 2015 that way if you do go Pro Channel you only not have the flyout EQ feature (or any future development of that type). But tech support might better answer that for you.

Why would you upgrade in the first place ? As far as i can see, you are very satisfied with x3e and how you work in Sonar.
I would wait until I found something to upgrade for, before I changed.
A new toy is always nice, but having two of the same toys would not benefit you in any way. If you buy in a year from now ,you will get the program with all the updates already inside. The only thing you would miss are the extra plugins,features that have also been added.
For the record ,I am not trying to talk you out of anything. You are free to do whatever you like.
I hope this makes sense.

Thanks for your points.
I'll probably wait a bit and just keep using X3 for now.
 

After working with Professional for a few days I completely forgot I even upgraded. I see very little change for me and stopped paying attention. All my projects seems to load and play without any difference. So the new versions are all about the extra plug ins and VST's. A few features were added like Mix Recall.    If you don't need them then nothing wrong with X3. It's certainly stable and does the job.
 
I upgraded from Studio to Professional so I got a bunch of stuff that used to be in Producer for free like AD2. Only $99 so was worth it for that alone. 
  

There are several "extras" that alone are worth the price of going to Platinum.
The AD Producer Pack alone sells retail for $199 and gives you 3 Adpaks, 3 Midipaks, and
3 kit pieces for AD2, and, even on sale is about $129.
REMatrix Solo is quite nice.  You get most of the Pro Channel Modules, and
the improvements to the program are decent.  AND, if 
you go to Platinum, you get the "Platinum Club" benefits included, which could
pan out to be quite "lucrative" over the course of the year if Cake holds true
to their model.

If I were going to go in, I'd go Platinum.  But that's just me...always the most
bang for your buck.

I upgraded from X3e producer, and very glad I did.  Like the new Rematrix (but it's in the ProChannel), AD2 for a change from my Toontrack oversupply, I'm liking the new control bar too... to minimize for screen space, and some other aspects that are new, that I really haven't delved into that much to give credible reports.  I "want" to think Sonar is behaving better on my system as well (thx StudioCat ;-) )...
Another aspect is that I *do* like to stay technically current, and it is VERY nice knowing I have Cake's best right now and will for a FULL YEAR.  I think in some ways, keeping up to date is important in many intangible ways as well...but that's another topic.
IF you can afford it...I'd stay on the top of Cake's heap and jump in.  Runs great, so no regrets there from this camp.

The vocal sync in Platinum is a game changer if you need to sync up vocals or audio (in a video project.)

There's also a score of minor fixes that make it more slick to use and improves workflow. Lots of little midi fixes

I think those fixes mentioned by mudgel are included in artist, too, so you'd still get those.