Honestly, tank wise, they are all the same. You can look in the stickies to find the weights, more or less, and since you are going to Myth it, then you have one very good small and light reg right there. As to how much less you are going to shoot, it really depends upon what you shot now, and how many shots you get off of a full 68/4500 fill. Because you are reducing the size 23 cubic inches, you could almost say that you are going to get around 2/3rds what you get now. Should not be that hard to figure out.
dxs and cp same tanks. CP has faster recharge. If youre gonna get a tank and change the reg, get the dxs itll probably be cheaper then the CP. But if going stock take the CP, DXS reg is big and bulkyy.
"An eye for an eye makes the whole world blind."