Don't be surprised if your stock spring doesn't get your velocity over about about 250 fps (or, possibly, below 350 fps). I know at least five people who bought shiny new spyders, came to the field all excited and ready to play, got to the chrono, fiddled with their velocity for about 20 minutes and started asking everybody why their marker wasn't working. You'd be well advised to buy a spring kit, even if you don't need it, somebody using a spyder inevitably will.