Hey Mike,
Just a few answers. The alita 40 is different from the airtech 40... after trolling some koi forums, I found that the airtech is where it is at. The alita has a good name, but the airtech seems to be the new kid on the block and it is taking names. Like I said, just from the pump curves, the airtech is definitely ahead of the pack.
As for the PSI requirements, I think it'll be split down the middle with the airstones requiring some of it (.50-.75PSI) and then the water level will also require the other part of it and depending on how large and deep you go, the water level could be taking up more of that PSI requirement, so there's nothing wrong with a solid PSI rating.
Bob,
To answer some of your questions. It seems like your skimmer will actually be larger than Mike's skimmer by a bit. Another factor is whether you will have a wetneck like Mike. I think that might change up your numbers a little. Honestly, for a skimmer of your size, I'd go with the Airtech 80 just to make sure you've got that extra power if you need it. If you were going with a wetneck, I'd think the airtech 40 would be a good match, but if not, go with the airtech 80. The four stones that Mike mentioned should do you well. The ones he mentioned are actually capable of withstanding moderate levels of ozone, but if you don't dose ozone then you can get the slightly cheaper polyethylene 1/2" NPT fittings on the airstones.
Peace,
John H.