Is it same amount? 1 oz pellet = 1oz. whole hop?
You generally want to add a little less (maybe 15-20% less) for pellets, but I usually don't really worry about it that much.
I would say that if the alpha is the same on both, then it would give you the same results.
They are pretty close to equal by weight. Pellets have better extraction as they are chopped up. However, the process comes at a price as lupulin is lost.
I'd say about 10% less IBUs with whole hops, as stated above, not much. If you're measuring out whole hops, measure out an ounce, add like 3 or 4 extra cones, and consider it equal to one ounce pellet.