Transition TransAM with an nos Judy, 63mm travel.

You'll have to run rim brakes on the front and a disc rear, but I hear that's a sweet setup for skidzzzzz.

All joking aside, you will have to go custom if you want a true mountain frame. As mentioned the cross check comes close, but it only has clearance for 700c x 1.8 inch rubber, you only get rim brakes, and it's not corrected for a supension fork.

Your first three reasons don't really seem that important, and I don't understand your fourth, but perhaps you could elaborate?

EDIT: actually the surly 1x1 has a fairly straight top tube, but it is singlespeed only.