Boolean Operations very slow

Hi,
I've a problem about opencascade boolean operations performance optimization

I need to display a box panel with about 100 cylindrical holes.

The code doing the job looks like :
___

TopoDS_Shape pannello = BRepPrimAPI_MakeBox(700.,-600.,+20.);

TopoDS_Shape *sottratta = new TopoDS_Shape(pannello);

//numero dei fori per direzione //numbers of holes
int nForix = 10;
int nForiy = 10;
//dist tra fori per direzione // gap distance
double distx = 10.;
double disty = 10.;
//raggio foro circolare //radius
double rag = 20.;

//gap
double gapx = distx + rag;
double gapy = disty + rag;
// ----
for (int j = 0; j for (int i = 0; i //a new hole
TopoDS_Shape* foro = new TopoDS_Shape(BRepPrimAPI_MakeCylinder(gp_Ax2(gp_Pnt(gapx*(2*i + 1),-gapy*(2*j + 1),0.),gp_Dir(0.,0.,1.)),20.,100.).Shape());

sottratta = new TopoDS_Shape(BRepAlgo_Cut(*sottratta,*foro).Shape());
}
// ----
Handle(AIS_Shape) aShape;
aShape = new AIS_Shape(*sottratta);
myAISContext->Display(aShape,1,0,Standard_True,Standard_True);
___
It works correctly but the resulting time to render it is very high.
It's about 124 seconds in my (quite new) machine.

Does exist any faster way to do this job?

If I change strategy:
// ----
for (int j = 0; j for (int i = 0; i TopoDS_Shape foro = BRepPrimAPI_MakeCylinder(gp_Ax2(gp_Pnt(gapx*(2*i + 1),-gapy*(2*j + 1),0.),gp_Dir(0.,0.,1.)),20.,100.).Shape();
*fusioneFori = BRepAlgo_Fuse(*fusioneFori,foro).Shape();
}
*sottratta = BRepAlgo_Cut(pannello,*fusioneFori).Shape();
// ----

fusing all holes in a single shape, before doing a single cut I cane save more than 40 seconds,
but 82 seconds are still not acceptable for my application. The goal is rendering the holed panel using less than 10 secs.

Does Anyone know a faster solution? Am I following a wrong sequence? Any suggestion?
Thanks in Advance.
Giovanni