So I am looking at either the

KB240
Bore (in):4.382 in.
Bore (mm):111.303mm
Piston Style:Flat top, with a trough
Piston Material:Hypereutectic aluminum
Compression Distance (in):1.908 in.
Piston Head Volume (cc):-5.00cc
Wrist Pin Style:Press-fit or floating
Pin Diameter (in):1.094 in.
Piston Ring Thickness:5/64 in. x 5/64 in. x 3/16 in.

or the KB280

Bore (in):4.382 in.
Bore (mm):111.303mm
Piston Style:Step head, with two valve reliefs
Piston Material:Hypereutectic aluminum
Compression Distance (in):1.327 in.
Dome Height (in):0.155 in.
Piston Head Volume (cc):0.00cc
Wrist Pin Style:Press-fit or floating
Pin Diameter (in):1.094 in.
Piston Ring Thickness:5/64 in. x 5/64 in. x 3/16 in.

I am confused as to which with help with the compression bump, oh and I have to go 40 over, already magna fluxed and sonic checked to make sure and they said it could 60 over with no worries. So which pistons should i go with ? and these will be going on stock length rods

THanks,

-Mike