My typical advice on cylinders is at the first link below, but once you've been playing a while consider the second link
http://p8ntballer-forums.com/threads/advice-on-starting-gear.158003/#post-1428729
http://p8ntballer-forums.com/threads/tips-for-getting-started-in-paintball.99186/page-2#post-1429740
If your site only fills 3000psi (like most sites) there is little benefit to spending on a 4500 cylinder
You could get fills from elsewhere
Whenever using a dive centre for fills make sure they absolutely know what they are filling
In dive shops they primarily use BAR not psi
300 bar is equivalent to 4500psi. People have blown the safety burst disk by wrongly filling a 3000psi cylinder to 300bar
Dive shop staff who provide fills should know better. The cylinder is also marked in bar, if they don't understand the marks then they should not fill
You can get your own scuba tank and fill station. But a 4500psi scuba cylinder costs more again
Is it worth £150 for a paintball cylinder and £300 for a 300bar scuba cylinder and fill rig so that you get an extra 1500psi? And that's only the first fill, the second in less, the third even less (as you take air from the source cylinder the pressure drops, the more air you use each time the quicker the fill pressure drops)
http://lips-paintball.com/acatalog/300bar-12ltr-Dive-Tank-with-INTEGRAL-FILL-STATION--221.html#.UaE_66a9K0c
If you are asking the question as to whether 4500psi is worth it then it is not worth it
Save your money and use 3000psi