Pump-action shotgun requires a completely different approach gamestyle wise compared to an AEG or pistol. Face to face you're not gonna able spam it like a hpa tapped short stroked pistol, feathered hpa engine or trigger response built AEG.
Joule output is more important in my opinion because 3 god forbid 6 bbs does hurt especially when it's a tight grouping.
Altough, your average speedsofter cunt puts the same amount into you in a milisecond so in reality it doesn't really matter.
Also, 6 shots aren't practical because you get out less trigger pull per shell/magazine plus the spread is crazy.
The other thing is that you have to be a real wanker to run it on 6. And sooner or later someone is gonna mention it to the marshall so there is no point to hurt others for some childish power fantasy.