I would go w/the Skyjacker Softride 4" if you plan on staying SUA, w/some 1.25" lift shackles. This is the basic combo my Dad has on his CJ-6 (1.25" lift shackles front, 2.5" lift shackles rear, in combo w/the 4" Skyjacker)., and it rides nice! Flexes awesome (had to put extended YJ bumpstops on so we can fit the 33's! The 29's were still flexing into the wheel well completely!), and rides smooth! It doesn't jar your teeth, and slam you back like the old worn out stockers did. As far as the Black Diamond, yes they are stiff as a board (wheeled w/a CJ-7 that had the Black Diamond 2.5" kit, and his axles barely moved! I got more travel out of my IFS!). BDS is good if you plan full trail gear, winch and 35x12.5 or larger tires w/widetrack or wider axles. They do work real nice in SOA though, as I've seen Nutter's Jeep wheel, and it seems to have the right amount of flex (not too much, not too little). So, in conclusion: SUA I'd go 4" Skyjacker, SOA I'd go BDS 2.5".