If I recall, wildfire recommended 3k psi. I went with 4k because the cost was not much different. Too much=ok not enough= uhoh
I would go with at least a 5" slab.
For what it's worth, my Rotary 4 post has huge plates under each post. It has been bolted in the same place for the last 5 years without any problems.
I built the shop that is sets in. The concreate floor is a 4 inch pour of a 6 bag mix and is reinforced with 1/4 inch wire mat, compacted 3/4 minus road crush base. The entire 40X54 ft slab sits on 3/4 inch rebar reinforced 12 inch footings.
To this day there is not one crack anywhere in the slab.
I can post pic's of the lift if anyone is interested.
