Mine is 5.5-6/8, getting ready to be 6/12.
5" is the max that you can go without getting into serious customization in the front and even at that level, you're going to wear the inner fender wells out from rubbing. 5" also induces quite a bit of bumpsteer and some geometry problems. The 7" in the back is also all I would go, I tried to go lower and ended up with massive pinion angle issues. Even at 7", the pinion angle isn't good but it's not dangerous. It's also as low as I would go with a standard c-notch. Any lower and you'll be riding bumpstops and the rear riding on bumpstops is not a good ride.
Of course, if you have money to blow, all of these can be corrected, but then you run into clearance with the ground, especially with the gas tank and crossmember.
I am gathering the parts to do it right now, but my advice would be to start at 5/7. That'll give you a good idea of the issues you'll have going lower pretty quickly. Mine sits a little higher than normal in this picture because I have air in my helper bags, which helps the ride quality a bit.