Considering adding a lift - thoughts on 2-post vs. 4-post?

I have a 9000lb Challenger 2 post lift, in service now at my home shop for 16 years. I have had 10,000lb dually trucks on it. They ALWAYS underrate the lifts, because they know people will test their limits. Mine gets used a lot, with never a problem. I have 14'2" ceiling in the lift bay, So I used a 2ft extension on top, in case i wanted to get a Conversion van or something, all the way up to wallk under...