Yes, both will fit the chipset, but make sure your enclosure can. They aren't small in length. Both cards are 10.5 inches long.
As to being worth it's price...if it's costing more than the 580, get a 580 for sure!
I assume you didn't mean it the way it's typed.
It's value depends on your need. What is your system and resolution that you use, and what games (if you game) do you play?