I would beg to argue the differences between the saz efficiency at 1 ohm rated output and the ZX efficiency at 2 ohm rated output. I would bet the difference is more in the 10-15% range, But conveniently, neither one of those figures are readily available for either one of us to support. Now, there is one little factoid available that you mentioned. The SAZ is rated for 250a fusing and 86% efficiency with 600 watts at 4 ohms....the ZX, on the other hand is rated for 300a fusing and claims 90% efficiency with 1200 watts at 4 ohms....how does that twist u noodle?