for 25 man raids, it's tough to say. You should have some Kara gear to pull your weight in Gruuls. I've seen people in there with some pretty crappy gear, and I'd imagine that there's less pressure on any individual person to have good gear, since there are 25 people in the group.
However, you DO need more HP for Gruuls than you need for Kara. Hunters typically tank 1 of the adds in the High King fight, and even though he doesn't hit very hard with his ranged spells, it's always a good thing to be easy on your healer. As for the actual Gruul fight... It's sometimes better to have PvP gear on, because after 5 minutes or so, you won't get any heals and will probably be expected to pot and bandage yourself. The ceiling caves in, and causes 1k+ damage every second if you don't realize that you're standing in it, and he has an ability called Shatter, which does a TON of damage if you're anywhere near anyone else when he does it.
For gear, I find that once you start getting some pieces from Kara, your AP will go down a bit, but your HP and Mana will skyrocket, making 25 man raids overall easier.
Post your Armory so we can see exactly where you're at.