Evan,
I wouldn't recommend getting just a spring and nothing else. You're not going to see much of any performance gain other than maybe a little more mid-range power (but not much).
If you don't need more low end, then go with a UNI filter and velocity stack/carb rejet like Josh got. It'll give you more overall power from bottom to top and you'll probably GAIN some top speed and definitely not lose any low end!
It's the level 1 air performance package on my site for GY6.