I am putting the rubicon express CJ 4.5" EXTREME-DUTY KIT on my 86 cj7.
Any advice on which shocks would be best with this kit?

Also, what does SOA mean?

I've had cheap shocks work just as well as expensive ones. ran a set of el-cheapos i got at Champion auto that outlasted a set of Ranchos, and the ride quality was the same.

SOA stands for Spring Over Axle. Simply put, the stock leafspring configuration on CJ's and YJ's is SUA (spring under axle) Look at how the axle is situated above the leafpack on your jeep. An SOA conversion moves the springs on top of the axle. This adds 5-6 inches of lift and flexes better then stock SUA configuration. It also makes it a different animal to drive and creates other problems that need to be addressed (high-steer, CV drivelines, extended brakelines, castor angle correction, extended shock mounts...)

I've had good luck with my Rancho 9000X.

My ZJ had Skyjacker hydro, decent and cheap but didn't ride very stiff.

My YJ will have either Rancho 9000s or Doestechs.