Are you needing to pierce at that thickness, or can you come in from the side? Pierce will be a lot less than cut for any given machine.
I have an r-tech machine which is a lot nicer than my friends clarke of a similar on paper spec, but still, i do not find that the cut depth is as good as the specs make it out to be.
But it will all depend on your budget. I guess low end, take a gamble on one of the cut-50s from an ebay seller, then somthing like an r-tech, or a bit up, tech-arc, and then if you want to spend money, a hypertherm.
I dont actually use my plasma nearly as much as i thought i would. Sure, for some jobs, its spot on, but for most cuts i generally choose a different method. But it all depends on what you are up to.
Id build a cnc plasma with a hypertherm if i had the space or the application for one (or probably just one of those would do, and then id make up the rest...)