Well, Alex, I am for the moment holding off on 8.1, but it is not because of a lack of a backup strategy.
 
For me, it is simply because I want to finish a couple of projects prior to evaluating reported issues with drivers and other potential 8.1 compatibility problems.
 
So, it is more of a time issue than anything - for me.
 
I will be setting up the backups and strategy for making that move when I get past those 2 projects, and will absolutely have a recovery strategy if things go South.  I should be ready to move to 8.1 in a couple of weeks, at the most.
 
If I have any issues prior to then, I will potentially seek to make the move sooner, depending on the evaluation of whatever issues arise.
 
Bob Bone

Bob,
I understand what you mean. My new laptop had gone through all the Windows updates before I installed X3, so although it was new it had a good period of time to settle down with all the various windows updates which I agree are many. This was all Windows 8 and I haven't moved to 8.1.
Appreciate your continued interest.

Thanks - TRULY glad it is working for you.  Wish this kind of stuff didn't happen to folks from time to time, but at least you are beyond it.
 
Bob Bone
 

Thanks for posting rloseven. This solution worked for me :) 
 
Interestingly I used the same X3 download on two PC’s
W7 laptop and Session Drummer worked fine,
W8 studio PC is where Session drummer wasn't installed correctly and wouldn’t  show Session Drummer in X2 and X3.
 
On both PC’s I firstly …
Suspend my antivirus software prior to installing. (Norton 360)
Installed SONAR 64bit versions only.
Logged in as an administrator
 
I had to do it twice because the first time I did not firstly remove the SD64 dll and after installing SD from X2 the X3.dll (1708 kb) file remained 
 
2^nd time round I removed the .dll and X2 install loaded the X2 SD.dll (1568 kb)
 
All is now good and can go back to work Yahoo!

It's important to note that once you've run the Microsoft redist (#34) and restarted Sonar X3 you must also do a rescan of the vst plugins (#4). This was the only way could get it working. Before the rescan it just continued to fail. I'm running Windows 8.1.