I have the SL6 and access to the Hexalite. I will take the SL6 every time. The Hexalite is reasonable quality, but not quite up to par with the Golite. The poles are very underdone, and I bent one in 5-10 mph winds. I now double pole every time. The Hexalite is much heavier than the Golite, but it is also bigger in every direction. It also requires more pegs and guys for anything approaching stable pitching. ThePentalite arrived today, so I will try to get that up this weekend to compare.
Edward, I'd focus on the SL8 if I were you. I've had six adults in the SL6, but that was either in the snow, or floorless, and sleeping rough. I think you'll struggle for 8, even if some of them are little. Plus, the SL8 will give you a buffer over the next 5 years.
Another option you might like to consider if you get no joy, is a couple of BD Megamids, with the doors facing each other and a tarp over the middle.
Either way, good luck and have fun. It sounds like you guys would be great to do a trip with!