Are my frequent Safari beach balls caused by my extensions?
I'd say it's definitely possible, if not likely.

For starters, turn off extensions altogether, to verify that they're causing the issues. Then I'd suggest disabling them one at a time (which sounds like you've tried partly), until you can isolate which one is causing the issues.

If that doesn't help (but all extensions off does), then try only one of your Javascript blockers at once, in the event that some conflict between them is causing problems.