The 2X2X1/8 tubing should be plenty stout. Any pattern you have will work OK, with the slight change I mentioned on the first one. The X pattern one would probably be best, as you said "hard to improve on it".
Those $127.00 hinges are for someone that doesn't know how to weld, or who welds poorly. If you fit the latter description, get someone else to buid the whole gate. You most likely don't fall in that catagory, so build your own in the same design and $ave $ome buck$. Those you showed for that smoker should do the trick, just scale up the dimensions to suit the weight capacity. By the way where are the pix of that smoker you said your working on? That can be a whole other thread right there. How come we're just finding out about it? Not ashamed of it, are you?