I can definatively say that the Ice Giants in Everfrost have just under 5000 hit points. Been killing them for the past few days and running the battles through an analyzer. My approach (level 51 ranger) is to root, dot, then shoot like crazy, root, dot, shoot, etc until dead, (the IG's dead of course, not me).
In every case, the amount of damage they took was in the 4900-5000 point range.
Loot can be maddening of these guys. I've gotten plat as high as 46pp but once I got 2 gold, 3 silver (Boy was I ticked off at that one!) Good amounts of gems and FS weapons over the course of 8-10 battles. Of course there are the occasional Ice Giant Toes and about 4 or 5 different kinds of 1-2 plat jewelry.