Have you played a game yet? If not, play a game and have a go of someones sniper rifle and see if you like it. Because you might not like the bolt-pull of a sub 500 fps rifle. Look here for more info: http://www.airsoft-forums.co.uk/index.php/topic/30038-budget-of-ll-lll-what-gun-to-choose/
Why not? I keep seeing new players wanting to get into sniping thinking that they'll be like Bodgeups/Novritsch and the likes, even though they haven't even played a game yet. The 'spiel' that people give is critical information for you new folks, they're doing you a favour and saving your wallet.
Back to what you are here for..
I've found that pre-upgraded sniper rifles are sold because the owners couldn't get them how they wanted them, so they might not perform that well compared to say a stock AEG. Ofcourse, that saves you money, and it might perform how you like it! If you don't like the heavy bolt pull, you can always get a Mancraft SDiK kit, which reduces the bolt pull distance, effort and is very consistent, you can run it via HPA or Co2.
It's a good idea to use BB's that are heavier than .30g, so they are less likely to be affected by wind AND so you can make more use of harder buckings so they can apply the most backspin possible, which equals more range. Certain hop-up units for the VSR allow for the use of AEG barrels, buckings and nubs so you have more choice to get the most of your hop-up.