If you know how many shots you get with a specific tank, you should be able to get a rough estimate of what other tanks can do using ratios. For example, if you want to know how many shots you will get out of a 48/4500 tank, the pressure is 1.5x the pressure of a 3000psi tank and the size is the same. That means that 400 * 1.5 = 600 shots from a 48/4500. If you want to know how many shots you get out of a 68/3000, you know the pressure is the same and the size is different. 68/48 * 400 shots = 567 shots.
Using ratios, this is what I estimate your shot count to be:
68/3000: 567 shots
45/4500: 600 shots
68/4500: 850 shots
These numbers assume that your 400 count is accurate and you are completely filling the tanks.