1) The Gigabyte EG41M-S2H is not a crossfire motherboard, it only has (1) PCI-E x16 slot. http://www.gigabyte.com.tw/Products/Motherboard/Products_Overview.aspx?ProductID=2945
2) IF you had a Crossfire motherboard, I would buy a 2nd 5770 since you already have one.
3) If that is an ENERMAX PRO 82+ 525W I would have NO concerns with the 600W power requirement it is a high-end and efficient unit. Even if it was one of the other models, it is probably perfectly fine. Enermax makes good stuff.