The ratio for an IIPA should be around 1.13 according to Designing Great Beers--though you are over this, it is still your beer so do it, but you can be sure you will get plenty of hop bite. It is not so much simply raising IBU's as the gravity goes up. You settle on a certain IBU:gravity ratio for the style and as the gravity goes up it takes more hops for the ratio. It takes more IBU's to maintain that ratio, but it's the balance that matters. Very strong Belgian and Scotch Ales have very high gravities and very low IBU's. For example Belgian Dark Strong has 1.075 to 1.110 OG and only up to 35 IBU. Wee Heavies go up to 1.130 and also top out at 35 IBU's.