£600 will go a long way, particularly in the classifieds on second hand ones
Consider not putting it all into the gun.
I usually tell people that aluminium / steel cylinders are the hat value for money, give sufficient air capacity for anything but the worst air guzzlers, are not always such a weight saving and most of the time you won't get a 4500psi air fill
However with your budget you could go to a fibre wrap cylinder as well. The real benefit of these is shape & size enabling you to perfect the ergonomics for you and balance your gun
Where are you based,where do you play etc?
Check this out and find the nearest shop to you, or nearby to somewhere you visit
https://mapsengine.google.com/map/edit?mid=zdRfWqkdmKGw.kbddocq_JqUY
Chat with the guys at the walkon and ask to hold or possibly try their gun on the range, visit a shop and check out what they have
Take your time before spending that kind of money