I agree with your water levels. I would want at least 650 cfs to put a small raft down the Upper, at least a grand for the Lower. While I agree that the rapids on the Upper G have different characteristics than the New, the lower feels very similar at comparable levels. If you are comparing release levels on the Gauley, the comparable would be 3' ft or a bit over on the New. Some of the Lower G's rapids are longer.