Orion/Peak was the only major matcher still holding onto the GP4300 and they finally caved a months ago because the IB cells were kicking their butt. Now GP4300's are on blowout at Stormer, another indication they are the lesser cell out there right now and IB is where it's at.
Not to say GP won't make a comeback but IB has proved they are serious and are making huge advancements in their cells. Look at the quick releases of 4200, 4200SHV, and 4200WCE all with huge gains in voltage, IR, and runtime with each release.