OP says this in first post: "Never had a problem with X3 - even when I recorded a 7 piece band recently with lots of plugs enabled. Today I've crashed non-stop"...
 
So the problem has started recently.  What changed?  I would troubleshoot keeping that in mind (If it's down to plugs, use process of elimination).

It's also possible that there is a corrupt file somewhere important. I'm not sure if a "save as", to a create a new instance of your project may help, but this has worked for me when a project has started crashing for no reason. I haven't been able to tell whether this is happening with only this project, or others as well, you don't specify.

have you tried starting a new project and replicating this ?
or is it one project specific ?

Your best bet would be to open a support ticket with Cakewalk and send them your minidump. They'll be able to quickly identify which plugin caused your crash and you can proceed from there. 

Thanks for all the help everyone!
 
I decided to dig in. Forced a few windows updates that hadn't taken place, updated my video driver, uninstalled some free VSTs I don't use, and did some trouble-shooting on Waves. I was having an issue adding C4 to a project. A Waves tech has been feeding me some things to try. Throughout all this I realized I had my 32bit VST folder in my scan as well as my 64bit VST folder (hence two Waveshell files). I don't think I actually use any 32bit VST files, so I removed that folder and rescanned.
 
Project is running great (and Sonar is loading a lot faster), but I need to let it idle again tonight and see what happens.
 
Again, thanks for all the pointers!

If it is freezing when idle, have you checked that you have turned all sleep options off on the usb devices that you need to stay active? If not, this could be your issue.
 

I have not checked that but I will, thanks!

That is USB Selective Suspend.  If you select the high-performance power plan, then edit it, expand the USB settings, you should see that in there somewhere.
 
I also set my min CPU to 100%, so my CPU is always running at 100%.
 
Lastly, 'Green' disk drives can cause problems due to something with the variable speed.
 
Bob Bone
 

Make sure you have the latest, 64-bit version of Amplitube. Amplitube takes a lot of CPU. There have been a lot of optimizations starting with Version 3.7; I think the latest is 3.10.

if it matters the 64bit version I run is 3.11.2