Yup, you pretty much nailed it.The smallest insert will give you the lowest possible FPS. Even if you max out your PSI to 280 with that insert, your FPS will be at indoor field levels. I use the green and haven't had a reason to change it. Some people use the blue when they get a 360 QEV. The silver is meant for indoor arenas, so don't use it if you're outdoors and stuff.