I bought a new Bendpack 9000lb 2 post A symetrical lift 6 years ago (when I had some money) and it is without a doubt the best tool investment I have ever made!
You want to make sure you double the thickness of your concrete where you plan to anchor your lift. I would recommend a pad of about 3ftX3ft.Where your post are going to land. You absolutely do not want to drill all the way thru your concrete when putting in the anchors!
Also make sure you locate the whole works far enough from the walls so you can walk all around it . I didn't do this and have to walk all the way around to get to the tool box when a vehicle is not all the way up!
My BendPack arrived last week,sitting outside until I get the inside of the shop ready. I like your idea about the 3x3 ft. of concrete,looked at a hoist installation last week that was done like that, better safe then sorry. It's been 28 years working without one, and chumping at the bit now to get at it!
Brian