Thank you @Marco. My experience with Cineform has always been rock solid as well but others have said XAVC is more stable in Vegas Pro.

Another question then: Would you stick with Vegas Pro 13 or upgrade to the Humble deal's Vegas Pro 14? I'm hesitant to invest even $20 if Vegas Pro 14 isn't 'any better stability wise than 13

I can't tell how much worth an upgrade to VP14 could be. More stable than VP12 or VP13? I'd say no, while on my system, there neither is a stability problem with VP14 or VP15. But for sure this differs from system to system.

See the list of enhancements and new features of VP14 to see what you'd get for $ 20:

• Added Smart Zoom, Smart Scale, and Smart adaptive deinterlacing to allow you to upscale clips for Ultra HD delivery (requires a supported NVIDIA, AMD/ATI, or Intel GPU).
• Added a Vignette video effect.
• Added support for working with high-frame-rate (HFR) clips.
• Added hover scrub to the Trimmer for fast scrubbing.
• Updated support for current BlackMagic Design hardware:
  DeckLink 4K Extreme 12G, 4K Pro, 4K Extreme, Studio 4K, SDI 4K, HD Extreme, Extreme 3D, Mini Monitor, and Mini Recorder.
  Intensity Shuttle, Pro 4K, and Pro.
  UltraStudio 4K Extreme, 4K, Pro, SDI, Express, Mini Monitor, and Mini Recorder.
• Improved support for clips from RED ONE, EPIC, SCARLET, and WEAPON cameras.
• Added Post lift, Post gamma, Post gain, and Dragon enhanced blacks controls to the R3D Decode Properties dialog.
• Updated support for current AJA hardware.
• Added a Resample mode drop-down list to the Video tab in the Project Properties dialog. You can use this control to set the default resample mode for your project video. To override the project resample mode, you can use the Force resample and Disable resample event switches.
• Improved playback and editing performance when using a Dynamic RAM Preview cache size greater than 200 MB.
• Improved gamma calculations for still-image sequence renders for 32-bit floating point projects. Now levels for 32-bit floating point (video levels) and 32-bit floating point (full range) with nonlinear gamma are more consistent with 8-bit levels.
• Added a Group Video and Audio Events script (Tools > Scripting) to allow you to easily group audio and video events from an imported EDL.
• Increased the top-end of the range of event Velocity envelopes to 1,000% to increase the maximum possible overall velocity of video on the timeline to 40 times normal speed (in conjunction with the Playback rate event property).
• New artwork and icons for buttons and other interface elements give the application an updated, more modern look and feel.
• Support for reading and writing HEVC/H265 files.
• Native support for reading ProRes 422 files without the need for QuickTime.
• Improved the Velocity envelope Set to functionality so that all points selected with the Envelope Selection tool will be set to the value entered for any of the other selected points
• Added functionality for reading and saving project media tags to HEVC and ProRes media
• Add new Velocity envelope presets (20% and 40%) to make working with high-frame-rate video easier
• Greatly increased the number of scripts that can be shown in the Scripts menu
• Added a general preference to allow users to enable legacy GPU rendering
• Expanded the low-end range of the sharpen effect to allow access to softer values
• Native support for reading ProRes 4444 files with full bit-depth
• ProRes rendering capabilities including presets
• Trimmer toolbar Add buttons and keyboard shortcuts now always honor the Trimmer in and out points
• Hover scrub improvements have been made to support quantization, snapping, and showing selection
• Support for reading HEVC hvc1 file variants
• Added ProRes rendering options for 24p, 30p and 60p/I framerate.
• Adjusted the horizontal tolerance for Trimmer window hover scrub to make it easier to add the selected area to your timeline without inadvertently establishing a new selection.
• 10-bit rendering has been added for HEVC files along with new 10-bit render templates and the ability to create custom 10-bit render templates

For $ 20 this may be a lot if you would use some of these new features. But if you would not use them, not much left to make you spend the money.
On my system playback performs a bit better than it did with VP13 (maybe due to the tweaks they made for the VP13 RAM preview buffer). Also it may be you won't get some of the plug-ins and scripts for VP13 anymore. But if VP13 already satisfies all your needs you should be fine.

I couldn't find that info - Thanks! I just ordered :-)

Good decision. The money is nothing. It is your time that is valuable - either lost fixing problems or gained with an NLE update. As you said, cs6 is getting very old.