SHould I install 8.5

The only reason I can think of to install 8.5 would be one that does not seem to apply for you based on your post; to use the pantheon reverb or V-vocasl. More and more of Cakewalks 32-bit offerings are deprecating and being replaced by 64-bit options. If you don't have 8.5 installed currently, i doubt you are missing Pantheon.  The same applies to any other plugin not offered past 8.5.  The DX offerings that are still included with X3 do not need 8.5 to function and the same gfoes for the  included 32-bit options that work via bitbridge.

LeBassist
Because you mentioned installations, I want to mention something here that I haven't seen on the BBS.  And to render it down....  "The sequence in which to install programs is crucial".  If you are going to install both, do 8.5 first.  It may be obvious, but there, I said it.  This applies to PC's in general, plan the install sequence.
 
One notable plugin that I miss that is in 8.5 but not X3 is BEATSCAPE.  I would miss that as the defunct replacement appears to the MATRIX.  Someone can correct me if I'm wrong.  Specifically, BEATSCAPE had the AKAI 16 pad layout, but it had adjustable parameters for each pad, even with effects.  Not to mentioned the segmentation screen on the bottom half.  Still a great product!

I would respectfully disagree that Matrix is replacement for Beatscape.  For starters, they are very different in form and function.  Also, Matrix view was actually in 8.5 too. This is admittedly oversimplifying both but  Beatscape was laid out like an  Akai MPC style drum sampler type instrument but certainly did not function like one. The Matrix view is not a plugin at all and contains no sounds of it's own.  It is more of an alternative method of sequencing that can handle midi or sound loops.  I think most would agree that it was meant to be more along the lines of some of the sequencing features of Ableton Live than and MPC type feature. Matrix is more of an integrated part of Sonar and offers more of a functionality option as opposed to being a loop mangler type instrument like Beatscape attempted to be. It also serves as a means to do some live sequencing, although not on the level of Ableton.  A true alternative to Beatscape would be one of the many MPC clone type programs like Groove Agent, Geist, MOTU BPM, etc.

koikane
Thank you for your help. Is there any need for a vst wrapper any more?
 

koikane.  I can't think of any.  Sonar handles VST natively now.

Here's what you'd gain by installing 8.5:
    Pantheon reverb
    V-Vocal
    FX2 Tape Sim
    Beatscape
    TruePianos Amber
    Guitar Rig LE
There may be more (Studioverb?), but these are the ones I can think of. I believe all of them can be installed without actually doing a full install of 8.5, although SONAR itself doesn't take up much disk space.

I installed 6 through X3 recently cuz I want to know anything used in any old project will be available. This way I know I have the latest versions and many of the thangs that are no longer included.
 
Used little disk space, and I have all the wav and flac files for DP,...