All my basses are four (except the Ibanez Studio) right now, tuned either standard or "down". They are all in storage right now, so I currently only play 12 string. The Chapman Stick Dual Bass Reciprocal. I know, I know, etcetera, etcetera, but once you play it...FOR A WHILE, it's easier than a standard bass. You tap with either hand. No calluses. (OMG). It's not like I'm gigging in a cover band...
Also. The last 5-string I had was tuned EADGC. I de-tuned the E manually when needed. Ho hum.