FWIW, GPO is very much an "entry level" orchestral VI. It is very good for what it is, and one can do very good things with it. However, as one starts to get into the world of orchestral mock-ups, and sampling, you will likely reach the point of wanting something (much) better.
Even the "lower end" good stuff: EWQLSO Platinum or VSL SE (let alone the full VSL libraries or EW's Hollywood libraries) will absolutely choke your system. Even for the VSL SE libraries, you need 8 gigs of Ram at a minimum, and at least a Q9550. For the better, newer libraries, at least 16 gigs of Ram is needed, and a 3930K processor would not hurt, though depending on needs, the 2600k would likely be fine.
If you are thinking about pursuing orchestral VI's, it is very easy to make mistakes (from personal experience) and spend $$$ on libraries that you end up not needing/liking. IMO it is a good idea to try to figure out the style(s) you wish to write in, and then determine what libraries best fit with what you intend to do (and the computer power you will have).