I know this probably won't help you much, but it really varies from one manufacturer to another. A M/F from St. Croix, for example, will typically be a bit "heavier" (power, not weight) than a similar model from Shimano.
Actually that does help, I have been reading and I do see that some companies are heavier then others, but it is hard to keep track of them all...so yes that is helpful, cause it tells me that if I go with a Shimano product I should get med/heavy with a fast action....
Looks like I am gonna end up with a few rods...lol...I am really making my self crazy...