If you're looking at protecting your benchtop I would go with a 2 part epoxy, like a deck coating. It will look really nice and take some abuse. Tho, well, if I were making a butcher block workbench... I'd want something that would protect that survace against scratchy, heavy parts. For this...
What works really well for a bench top is the same thick polyethylene used as commercial cutting boards in kitchens - we used to get custom made "plates" of this 3" thick and use it for push bumpers on the front of tow trucks - it would both be tough enough to take the punsihment of daily use as such and not wear out and not damage the vehicle we were pushing. IIRC these were a few hundred bucks each, but they paid for themselves the first time we *didn't* screw up someone's custome chrome bumper. And, oh yeah - they clean up really well with a steam cleaner.
Make a slot under the bench to store this polyethylene "cutting board top" so when you're pulling a motor, rebuilding transmission shafts, etc., you can grab it, drop it on the bench, and protect that butcher block. And if it ever gets totally gross or chewed (in about 10+ or so years) get the top reground - or chuck it and replace it.