Battery charging question

Ok, battery charging question, charge controller aside. This is more for my curiosity and general knowledge as I'm fiddling with that mechanical charge controller again and I'm trying to figure out appropriate charge rates in order to adjust the unit for best performance. (IE, adding or removing windings to get the desired effect) And yes, it's another one of those "I've got nothing better to do so I may as well learn something" projects.

Alright, anyways, I've done some digging and came up with this formula for battery charging. (Note: The suggestion states that this is "best practice" but not the law of the land or anything like that, just FYI)

1. Bulk charge flooded batteries at the C20/5 rate. (IE, one fifth of the total capacity of the battery in amp-hours at the 20-hour rate).
2. Charge AGMs at the much faster C20/2 rate. (ie, up to 50% of the 20 hour rate)
3. Gel cells must be charged at less than C20/5. Preferably C20/6 and below.

Now, given this information, my question would be, is this correct? Or should my charge rates be different for each of these battery types? The rates sound right based on what I've read on the sides of different batteries I've encountered (such as the 2amp max charge rate on my 9ah AGM's) but I figured a second and possibly third opinion wouldn't hurt. My idea here is to have a rule of thumb I can use when actual OEM suggested charge rates aren't available for me to reference. Thanks guys. You're always hugely helpful to me.