From experience, I can tell you about both ways. I originally did my 4-6 with DJM lowered CAs, a 2" spring (which I later cut and extra half coil from-it rode better too)and KYB shocks in the front, and a flip kit in the rear (also DJM). Had to roll the fender a little all the way around and had no rubbing problems. I do remember fighting the alignment for a bit, but finally got it to go where I wanted it. Road like a Caddy and handled like a Vette-a 4500lb Vette, but a Vette none the less. Was very happy with it. I do remember not liking the look of the steering link BJ spacers, but installed them anyway. One of them snapped off at 70+ MPH going around a corner and left me stranded in the middle of the night (not to mention a couple guardian angels with multiple contusions). I took them off the next day and lived with the slight bump steer for a couple years. About two years later one of the arms snapped just driving down the street. DJM wouldnt honor the warranty (even though I had been working for a DJM dealer when I bought them), and as I didnt have the time or money to buy another complete set, I picked up a set of spindles from a friend. They were Bell Tech and I was aware (from the many trucks I had lowered) that BT spindles spaced the wheels out a bit, but it was all I had. They rode great, handled great, aligned great and had no bump steer. But even rolling the fenders more (and tweaking them out as much as possible, I had rubbing issues. This isnt a problem with other brands of spindles. The reason that BT did it (and, for the life of me I cant understand why they wont admit it) is because when the lowering craze started back in 88-89 with our GMT400s, the biggest custom wheel readily available was 16". And spacing the wheel out a bit made trimming the stock LCA minimal. They just never re-engineered them.
If I were to do it again (for myself, that is), I would definitely go with the spindle/spring (non BT) and never look back.