You want huge hop flavor and aroma for IIPA. I dry hop 5 or 6 oz for AIPA , and usually a couple dry hop additions of 4 or 5 oz each (~7 days each) for IIPA. I like the choice of hops.
What temp are you dry-hopping at?
I recently went 7 days on my second addition at kegerator temps and now regret it. Day 3 was great. By the time day 7 rolled around, the aroma and flavor had turned from hop oily to hop leafy, tasting rough and astringent.
Rereading Mitch Steele's comments on dry hop additions, I came across the following (reply 43 in Ask the Experts): "I’m finding that 60-65 °F or so seems to work really well for us. Too hot, you might extract flavors you don’t want, too cold, you won’t extract enough of the really good oils, and as someone mentions further in the questions--you could get a lot of grassy flavors."
I'm going to follow this next time, hit that temperature sweet spot and limit exposure to 5 days.