Help with Spyder Xtra??

Im just getting into paintballing and want a starter gun. Ive thought over Tippmanns so i dont need any suggestions for them. The Spyder Xtra seems to be a solid gun from the reviews ive read. However one problem is that people have said that it is around 300 fps out of the box and i dont want to mod it to my field standards. The only reason i am getting a XTra is because of the min expansion chamber. I dont know if its that effective but if i splurge and buy a HPA/N2 tank, should i switch to a Spyder Pilot or Sonix maybe even an electronic? Im very confused here because im sort of a control freak and i have to know every single detail before i buy anything. Also, i would like to know if the mentioned guns can take a 3000psi tank... Last question..whats the differece in the 3k and 4.5k psi tanks? i Mean i know that they are different Psi's but how do they effect the gun? Thanks