I would say that people are building 2" thick concrete slabs for countertops all the time. With chintzy cabinets underneath to support them. It is about area of support as much as stout members to support.

Logs: I have a number of davit cranes and a couple engine hoists in my shop. My primary engine hoist is capable of about a ton. That's more than double an 800# log. For my 5 x 10 I installed a hoist on a beam trolley at the end of the machine. I figured that an electric machine that I could hook onto the product to be lifted was best... I can lift off the truck bed or off my trailer. My trolley rail is welded to my iron beams in my ceiling, and runs from the roll up door to a few feet down the machine bed. I don't do logs- yet. I am thinking I will keep all the components from the upgrade and start planning a franken bot for that....