You can take a look at the manuals for them, but they aren't all that helpful. The configuration utility for setting up RAID isn't really difficult to navigate, and we can help answer any questions you have.
The PERC 6 supports RAID 6 and 60; other than that, there may be some subtle, undocumented improvements in the 6 over the 5. Unless you want a RAID 6 or 60 or unless you happen to have an unused PERC 6 laying around, it probably isn't worth much $$ for the upgrade.