I went through this same process when deciding what I should do. I swapped in a D60/14BFF combo also. I wanted to run 38 to 40" tires but as far as the final outcome, yours should be pretty similar to what mine is (well, will be when $$ allows).
In all the searching I did, the answer I kept getting was that the best combo for that, if you aren't afraid to get cozy with a sawzall is to do the 4". Then, if you need an extra inch or two (don't we all
), you can add a zero rate and possibly a 1" body lift.
It's not a definite thing, but the "issues" associated with a 4" are potentially significantly fewer than with a 6" (think driveline modifications). Also, the 4" lift will ride better than the 6".
I did a DIY4X shackle flip in the back with 56" springs out of a Suburban, plus a zero rate moving the axle 1" rearward. I used 6" cross-tied shackles with the flip, also from DIY4X.
Up front, I ordered a set of ORD custom springs with 5" of lift and the center pin located so as to move the axle forward 1.5". These were spec'd for future addition of a winch and a reasonably beefy winch bumper in terms of weight rating. (I'm sure you already know this, but while you're under the front, you should look into the steering brace and frame reinforcement from ORD if you haven't done that already.)
With the setup I described plus some trimming, you should have plenty of room for those 37"s, plus it should ride nicely for you. You obviously don't have to do the custom front springs, but it is supposed to make a big difference in ride quality (don't know--I haven't had the opportunity to ride on them yet).
Hope this helps. There are lots of folks here with tons of experience on this. Many have tried several different setups and can pro/con each for you better than I can. I'm sure some of then will chime in shortly.
