Question with the JE Piston in the Evo engine

[Dogtor Evo]

Hi,

I am thinking about upgrading the piston in my M3 Evo engine, I would like to know what will a aftermarket piston do to the engine? and will i be gainning any hp? How will changing a piston affect the driving? Does it worth to do this upgrade since the Evo engine is pretty max out and very hard to upgrade the engine. Thanks!!!