I ran all the tests again with the new betas. I only found one minor bug on this go round and it's not really a bug as much as an inconsistency.
When I installed just the new beta of Form Builder, everything worked perfect.
When I added HTML Editor 3 and then did the simple contact form, when I switched the textarea to an instance of HTML Editor 3, the preview area simply did not show a holder for HTML Editor (it did previously when just the new Form Builder beta was installed). Instead, it still just shows a textarea box.
So, not really a big deal - but an inconsistency. The extensions however worked in accord with each other.
If you want to view any results, they are here:
Now on to some more intricate testing.