The last time I built my 540 in my boat I went a little looser on piston to wall clearance on Diamond pistons advice even though I had good results with J/E previously at less , (first time I ran their pistons). At .002-.001 down in hole they contacted the heads with carbon enough to rock the piston and harm the ring seal with a .040 MLS style head gasket,I will be running a little more quench this time around!!

If you are running a full dished piston verses one with a quench area, according to my engineer at CP and what we have seen on the dyno, the full dished piston will make more power. Now this is only in reference to a forced induction set up, if I remember it has something to do with the flame travel and the efficiency of the chamber.
As far as piston rocking goes, the barrel shape can be changed and the area between the top and second ring can be expanded to control rock. Depending on stroke, rod length and pin location all of those things will effect rocking. If you have excessive rock at TDC, go check your piston at BDC. When that piston changes direction at BDC that piston can rock so bad, you will prematurely wear the skirt and widen clearance.
I have seen a 10.200 DH, 4.625 stroke, 6.535 rod with a poor piston design, eat the skirts up ! That combination, was changed to a 4.500 stroke, 6.535 rod and some custom pistons, engineered to prevent piston rock. It's even more critical @ BDC when the skirt is hanging out of the bottom of the cylinder.

Ever tried a full dish with a couple degrees of slant in the dish towards the exhaust valve? All the big horsepower stuff I've seen had that type of piston in it. Don't know how effective it would be on a pump gas blower deal. But it's definately worth something.

Nothing like keep it simple. It seems challenging the 6k barrier gets complicated or better said .....money.

MER are you referring to a concave dish style piston? The ones that have a small flat around the entire edge about .200" wide and then has a concave shape for the dish? If so, at what psi of boost and HP range should you consider this style of piston?
i talked to a couple piston companies and all of them said i don't need that if less than 15PSI boost.. what everyones thoughts on this?

They may be correct on not necessary, below 15 psi, I have seen power increases on forced induction and a change in fuel MAP, requiring less fuel....It comes down to the efficiency of the fuel burn. Yes; the pistons are of what you described.
I freshened up two engines, that had 9.0:1 cr, went to a dished piston lowering cr to 8.0:1 increased power, and removed fuel....