The GTX cam is only found on target bows, the other option on target bows being the Spiral cam which is more aggressive (and faster) and only has 65% let off. Target shooters usually shoot lower poundage and like the crisp feel of the higher let off. GTX has a mod that lets you change a mod from 65% to 75% let off.
Hunting bows usually have more let off because the hunter shoots more poundage, and needs to hold until the animal presents a good shot. The hunting cams have a more generous valley, but recently cams have appeared like the Turbo that are so aggressive that the valley disappeared. The new defiant cam is soft and forgiving (you see the lower ATA of 325) I like the Z5 cam a lot it is very nice, easy to draw, and has a nice valley. Another thing to consider is your draw length and what position you will need on the cam an "A" position will not roll the cam over as much as a "E" position. The "A" will be easier to pull, slower and have more valley. You will use a different position on a different ATA length bow with the same cam.
I also have a 31" draw my favorite bow is a 2013 Carbon Matrix with the RKT cam on the "E" position. This is the forth offering (and the last) in the Matrix series with a 35" ATA (they went down to a 34" ATA and a Z5 cam with the Spyder 34) The Matrix shoots better than most target bows, has a cam that is "just right" good valley, but crisp enough release. and it is very light and well balanced. These bows are very desirable and hard to find, but worth the wait. Hoyt makes LD bows that you can shoot, they are the same bows with an inch longer limbs to increase the draw length. In general look at the IBO speed rating of a bow, the faster is is, the harder it is to pull because there is no free lunch. Hope this helps.