it doesn't exactly go by "Stage" each has its own advantages and disadvantages.
S1s are for the GA16
S2-S5 and C1-C6 are for the SR20
S2-S5 - street cams - higher # means the cam is more extreme, lobe size and duration is listed on JWTs website. S5s are more extreme than S3s or S4s. More extreme = more high end power, consequently, less low end power and more lopey idle. The S4s are about 5hp more than the S3s, the S5s are another +5hp or so from the S4s. S4 and S5 cams don't need it, but it's recommended you get valve springs and retainers.
C1-C3 - race cams(somewhat streetable) - more extreme, more lopey idle, require springs and retainers (a must). high-end power.
C6 (I've only heard of them) - Full race cams (unstreetable) - unusable low-end, crazy top end power.