Typically I have always put higher delay weapons in off-hand and lower delay weapons in primary. Due to the fact that off-hand tends to fire less often than primary. And when it doesn't fire all the time, that's ok because maybe the delay hasn't reset anyway. But if you have a faster delay weapon in the off-hand, and the off-hand doesn't fire when the delay is ready, then it seems like a waste of a check as you won't swing.