I think it is possible to get a decent ride with 4" lift springs, depending on manufacturer, and shackle angle will also be critical for a good ride. Any time you have a spring that is thick enough and arched enough to hold the rig 4" higher in the air, it stands to reason it is going to be a much stiffer spring and will not compress as easily or droop as much, so overall suspension travel is reduced. Stills works Ok though, just not as much travel and a stiffer ride.
SOA, if done properly, allows you to use a soft spring with more up/down travel/flex while giving an overall smoother ride. It also gets your pinions up out of the way and less prone to being a rock magnet.
However, to do it properly requires a whole lot more work and expense. The improvements in ride, handling and wheeling ability are there but are only incremental. Thousands have done the std 4" lift and are happy with it. In the end you need to decide how you will drive and wheel the rig, then decide how much money and effort you want to put into it.
Randy Rosetta KDØKWX TLCA #19351 NOW 2015 Rubicon Hard Rock & (2) 1970 Boss 302 Mustang's THEN 69 FJ40 Buggy "Meanie", Mini-truck "Gecko" & 74 FJ40 "Blue Mule"