I have a BendPak lift in my garage with 11' ceilings. You can raise a 911 to full height without any issues. Look for the floor plate models.
5" concrete with # 4 rebar 18" OC is plenty. The connection to the floor is the weak link. The bolts will tearout before the concrete fails in compression.
Bendpak provides expansion anchors. I would use Simpson set-pac epoxy. It is way stronger. Mcmaster carr sets insert that you can bond into the concrete. If you do it this way, you can bolt it down. If you ever need to move it, you are left with tapped holes in the concrete.
My Cayenne fits under the car if I remove the front wheels.
