Are you running stock axle assemblys under your JK?
Wouldn't 39" tires in any configuration be pushing it?
What Tubby said.
I have the blue label krawlers, but only in 35" and love them. My jeep only see's pavement when it's driven to the trails, so the krawlers have lasted me over 5years. also, the krawlers only perform at lower psi, so be prepared to run them on beadlocks, otherwise you'll be very disappointed. Like most bfg's, sidewall is still a weak link, so you'll need to be mind full of that when your on the trail.
If your jeep is a dedicated trail rig and see's little pavement, go with the blue label krawlers and have them siped (better traction off-road, runs cooler on the street) and they have a softer compound, but noticeably heavier then the KM2's, and a tad more expensive. Downside, is they're not great on the mud, and they are as loud as a boggers on the highway.
Km2's if you plan on driving it on the road. harder compound, lighter, cheaper, not too load on the highway and from what I've read, may not perform as well as krawlers off-road. At 39" or 40" on stock axles, be prepared to be changing wheel bearings monthly, but I'm sure you knew that already.
If skies the limit, then go with Red Label Krawlers. Tires are insanely soft and sticky.
You should also look at the new MTR Kevlar's, there seems to be a lot of buzz on the internet.