If you want that kind of weight capacity, I'd suggest stand-alone steel shelving. I scored A BUNCH of commercial-grade stock room shelves from a store at the mall that was going out of business. I've loaded them up really heavy. They have metal frames that knock together, with fairly heavy press-board (not MDF, not particle board) shelves. I think I got 6 of them (8 feet tall) for $80. Don't remember for sure, and don't want to run out into the shop, the basement and the garage to count them up! I painted the shelves with two coats of gloss white paint to seal them, making grease and oil less likely to absorb.
One down-side: The store I got them from was a candle shop--all kinds of sceneted candles. So every now and then, when the temp is right, the back corner of my shop smells like the shop was done by the Queer Eye for the Straight Guy crew!
After I got those shelves and loaded them up with parts, I scored some mid-duty industrial shelving. It's deeper than the stock room shelves, but I have TONS of weight on it. Maybe literally! Three manual transmissions (two iron cases), a set of small block cylinder heads, about a dozen 12-inch finned aluminum brake drums (20lbs each), some control arms, three aluminum intake manifolds, a '54 Buick radiator and shroud, a flywheel, and the list goes on. And on.
Like I said, they're deeper than I'd want in a garage/shop, but with them being as deep as they are, I can roll engines under them front-to-back, so I'm making the most of any floor space lost.
If you shop around at industrial places, you can often find used pallet racks and industrial/light industrial grade shelving at very good prices, and many times the heavy duty units can be had in narrower depths, too (18 inches deep is what I prefer).
Hope this helps a little.
-Brad
