I have a Stumps Baby. Bought it on 10/1 and received it on 12/23. To your questions.
Rack Spacing.. I have four racks but I think the 2011 models are three racks with four runners. The very top rack is basically good for only jerky. Depending on your butt size, the butts should fit between the racks. I have three butts in my freezer and the thinnest one is about 3.5". So it would be a tight fight to get them all loaded if you do not remove the rack above. If you take out the 1st and 4th rack, you can fit 6-8 butts. Which is plenty if that's all you are cooking. I don't think you would have a problem with briskets.
I don't cook a ton of food at a time. I've never used all four racks during the same cook.
Prior to purchasing the Stump, I did look at the superior, dw cookers and the backwoods smoker. At the time, the stumps was a bit cheaper.
I believe all of the insulated cookers, especially the stumps and superior claim you can get 8 hrs or so on 5 lbs of lump. I've done two all nighters and i filled the chute around 11pm and when i woke at 5 and it was time to add more. The temps stayed steady at 235 and it was in the 40's both nights that i did the cooks.
I am completely satisfied with the stumps and i would probably purchase another one. If you can swing the Prince, I would go for that one. I didn't want to spend $2800 for a smoker so i opted for the cheaper one. It does cook some amazing que and I have yet to be disappointed. Temp control was a bit of a learning curve for me, but I've been cooking on the baby every weekend since I got it. I also have a BBQ Guru, which I highly recommend.
Most of these manufacturers offer specials during the year. You may want to try and negoiate a price when you contact the manufacturer. Another factor is Stumps requires a 50% down payment at the time the order is placed. Not sure about the others.
Good luck and if you have more questons, shoot me a pm.
Bubba Keg / Stumps Baby / Super Fast Yellow Thermapen / Lodge Cast Iron Grill / Smoke Vault