All of my guns are IR composites (I own (4) 1/2" guns, and (2) 3/8" guns...)
IMHO, I don't care what the claim is on power rating, but any guns that's muffled to make it quiet loses power---I use my IR2135QT and it doesn't get some fasteners loose, break out old faithful (Matco IR2131) and it still rips after over 12 years of abuse!!!
On a side note, Sears sells one their Craftsman lines in composite (which is IR--I know, cuz I have one, and save for the chrome anvil/head, it is IDENTICAL to my 2131....but cheaper!!!