N8: I don't agree with your analysis. If you divided the 8,000 lb load for the entire area of your loft then you would need some way of transferring that load evenly to every joist and uniformly on every joist to make that assumption valid.
For that kind a weight, I would be running at least a 2x10 joists at 16" spacing. But with that kind of weight, I'd be adding extra redundancy beyond the joist calculation and beyond the joists to the entire building framing.