I went from BP51's to Kings 3.0's
The ARB shock were very nice, the ride was good but the front bearings i blew out twice and blew the rear seals too but im also VERY heavy all the time. The squeaking and noises meant they just weren't for me
I was one of the first to get the 3.0's front and rear. I helped with the development and install as they are a massive shock and not a simple bolt in and forget. Bump-stops need replacing, spring choice critical, diff drop (larger than usual) and UCA issues but we made it through. I wasn't expecting a huge ride improvement but damn did i get one, slow sped, fast speed, hot, cold these things outperform everything ive every ridden on and ive driven with Icon (not recommended), as well as the usual oil filled tin can shocks.
Do you need 3.0's, well in most cases no, they are complete overkill and most ppl wont find the limits of a 2.5. I do push the limits of my car, am often airborne and travelling very heavy on bad roads for hours on end. There is no harshness at all, no shock felt through the car when i hit a washout, nor when i get it airborne out the other side and land.
The BP51 is a nice around town shock that can do the trips away and makes for a very good ride. Id still run them in some applications and the company support and backup is awesome.
If you will be carrying more weight, pushing the car harder then the kings are a step up for sure. Its doubtful you will need a 3.0 unless you are wanting to really push the car past its limits.