I recently rented a Sandpiper sit on top and paddled it 10 miles in a small, slow moving river. I was with a group and was thus able to compare it to Old Town's enclosed cockpit models during the trip. The Sandpiper is light at 33 pounds but stable. It is rated at 225 pounds capacity. I am 6'4" and 210 pounds. With a little gear I was near the weight limit. However, I think that the Sandpiper can carry a little more than 225.
I was a bit handicapped in the top speed area. Loaded to the max, the Sandpiper was still quick and nimble at cruising speeds. The only evidence of a heavy load was the production of a bow wake as it "plowed" at high speed. This slowed me down and let the other kayaks outpace me. However, I could catch them when they encountered obstacles and shallow water due to the Sandpiper's agility and shallow draft. Not to mention the carrying handle.
This little boat gets a 10+ for fun. The seating position is the most comfortable of any kayak I have ever seen. You sit slightly reclined back with the high back seat supporting your own back. It is a bit like a recumbent exercise bike's sitting position. This position increases both comfort and stability by lowering your center of gravity. If you have back pain, you must try a Sandpiper. Or if you are like me and like to cruise and relax, the Sandpiper is hard to beat.
At 6'4" I was not cramped at all on my 10 mile trip. You can stretch your legs straight, lay them on the deck and still paddle fine. Not that I needed to though. The regular sitting position is fine. There are some trade-offs for having so much comfort. The sitting position is too low to allow self-bailing holes. There are none. Also, near capacity as I was I noticed that water lapped over the side a little if I turned 90 degrees quickly as in a "trick" move.
In summary, the Sandpiper is a great recreational yak for slow to moderate waters. At a retail price of $299 from a major manufacturer like Old Town Canoe, it's quite a bargin.