Not all paintball tank are created equal, there are different brands, varying volumes and also different maximum pressures they can hold 3000 PSI or 4500 PSI.
Today paintball tanks are made from two different materials aluminum and carbon fiber. Aluminum compressed air (HPA) tanks are normally the budget option and start at are $50 like some of the tanks below, normal these are easy to spot because they are flat bottom and stand up. In the paintball industry aluminum compressed air tank are always 3000 PSI.
Carbon fiber tanks on the other hand are much more expensive, but come in many more size, are much lighter and they are able to hold up to 4500 PSI.
Most paintball tanks are designed to have an output pressure of around 750 – 800 PSI. So if you buy an aluminum HPA tank or a carbon fiber HPA tank they are are both going to have the same output pressure. In other words the advantage of the 4500 PSI tank is the extra 1500 PSI worth of pressure, that address pressure adds up to 33% more shots. The 4500 PSI tank will not shoot further, hard or more powerfully because it outputs the same 750 – 800 PSI as the 3000 PSI tank.