I hear you there....But I never have the guts to mix cab impedance....I was always told that was not a great thing to do. The math works though, so what the heck!I run what Mesa Boogie would call a safe-mistmatch on my JCM2000 DSL50: its running an 8 ohm cab and a 4ohm cab at 4ohms on the amp. Comes around 5.3-5.6ohms when its looking for 4, so its slightly more but over the threshold rather than under it