https://github.com/jp9000/OBS/releases
download .658b zip, unzip the correct version (x64 or x86) over your obs folder
Keep in mind, this is a 'dirty' rollback, at some point you'll want to do a clean uninstall/reinstall, but I didn't have time before my next scheduled stream to worry about losing all my settings and it worked.
Really, I don't care if they want to pretend this isn't a problem with OBS (these optimizations don't work on some cards, retain the alternate, if slower, fallback option...), but it means that the code that isn't working on my card will probably be used in OBS-Studio and I won't be able to use future versions of OBS-studio until I buy a new graphics card (and roll dice to find out if it is stable under obs), which is frankly rude.