I ran an i7-3770(k) for four years and though I tested my old GTS 450 in the system when I first built it, that was the last time I every seriously considered running a newer nvidia card with Vegas Pro.

Look at sections 16 and 18 of this FAQ for a wealth of knowledge on this subject.

Does anything in particular make it crash?

What driver version do you have installed for your GTX 660.

Troubleshoot here: https://www.vegascreativesoftware.info/us/forum/faq-troubleshooting-crashing-and-stability--104785/

I've had constant problems with editing my Panasonic GH5/4 footage but today for the first time, I'm trying to render footage from my Sony Ex1 recorded on Atomos Ronin in ProRes LT to MPEG 2 for Architect Pro. It starts to render but then crashes every single time.

I spent so much time and money upgrading my Vegas, Windows operating system, and editing plug-ins for the 2017 season and as of now, the system is nearly usable. If changing video cards is going to stabilize the system, I sure would do it in a heartbeat at this point.

GeForce GTX 660 Version 381.65

Have you tried this?

Yes. And it worked!! 1:09;10 video rendered to MPEG 2 in 0:57:58

So, would this indicate maybe a different video card would be a good idea in the future?

If preview runs at less than real time with the fX on the timeline with GPU aceleration off, you probably would benefit from having a video card that you could leave on while rendering. You won't get any gpu assistance with MPEG-2 except for decoding the timeline.

Try rolling back to driver 376.33. Things went a bit pear shaped with Vegas for many Nvidia cards at 378.XX and sounds like they still might be for yours. That older driver might enable you to use GPU acceleration again. See this comment for a recommended roll-back process that includes using the Guru3D Display Driver Uninstaller.

If you switch cards, AMD generally work better with Vegas than Nvidia. As already mentioned, see this post for more info.

Try rolling back to driver 376.33. ...

Or to the 372.90.

Everything 378.XX and above is an utter mess. I haven't even got an image in preview window with those drivers.

Everything 378.XX and above is an utter mess.

Not with me, I have 381.89 no problem at all.
De latest one 382.33 is starting to give problems with the New Blue Titler OFX

Which model GPUs?