Those 17x22 sheets are priced at about $3.80 per square foot, versus the $1.35 I pay to my local supplier for 4x8 sheets. About a 3x markup. But hey, convenience is worth something and it costs something to cut down those sheets. Maybe I was being too harsh with the "crooks" designation. They are merely Mafia wannabees.
Gator is a prime example of stuff you should be buying from a local supplier. For my local supplier, I can buy a case of 15, 4x8 sheets for $0.00 shipping and they deliver for free. If I order it in, I have to pay the minimum freight charge of about $150.00, and about 10% to 30% of the sheets will be somewhat (or hugely) damaged by the notoriously gentle handling it received on the shipping docks and trucks. The avoidance of shipping is worth something, even if you find a technically better deal online, which you probably won't. I know a guy who drives 300 miles round trip from Northern New Mexico to pick up his Gator at my Albuquerque supplier.
3/16" is fine for very large prints. You're probably OK up to somewhere around 36 x 72 inches. A lot depends on how you're going to present it. The vertical dimension is your limiting factor since it is subject to sagging. For instance a 30 x 120 x 3/16 mounted canvas would be just fine, but a 44 x 120 x 3/16 would probably be a bad call. All that assumes the pieces are rigidified by frames. If you are presenting just a print on Gator, you would need to go thicker at much smaller dimensions.
1/2" or thicker looks better for cosmetic reasons, especially if you want to wrap the print around the back a la gallery wrap. For extremely large framed pieces the Gator becomes the major structural element and essentially carries the frame along for the ride, at least in cases where you are using polystyrene frames to keep the total weight under control. In certain cases you may need to hang the piece from the Gator rather than the frame, that's when 1 inch may be called for, and that will make a dent in your credit card.
Edit: oh yeah, the user-cut edges of Gator can be like very sharp serrated knives, especially as a result of sloppy cuts. Watch out. If you handle Gator you WILL bleed, sooner than later. Always know the shortest route to your bottle of Bactine and box of bandages. When you grasp a cut piece of Gator, be darned sure you don't let it slide against your flesh. Always say to yourself, "I'm gonna hold on to this piece of Gator very firmly, and it's not going to slide along my fingers, because I hate the sight of blood, especially when it's my own." 'Nuf said.