I finally found a German guy that had put a Cobalt/Saturn M62 on a R53, GP1 actually, and got a good tune with it. He posted up up a video and the power gains, 311 ps, are quite good when one considers how cheap they can now be purchased here in the US. Cheap enough that within the last week five more have been shipped over the Atlantic to join four that I sent over a couple months ago. In a couple of months there should be more dyno data out there with both stock and BVH heads.