Theas thread helps with performance issue a lot.
http://moi3d.com/forum/messages.php?webtag=MOI&msg=6440.1

script: /*SAVE SELECT TO STYLE*/moi.command.execCommand ('var gd = moi.geometryDatabase; var activstyleidx = moi.geometryDatabase.activeStyle; var objects = gd.getObjects(); var savedobjsnum = 0;var si = moi.geometryDatabase.findStyle( "selectset", true ).index; for ( var i = 0; i < objects.length; ++i ) { var obj = objects.item(i); if(obj.styleIndex == si){ obj.styleIndex=activstyleidx; obj.selected=true; savedobjsnum +=1; } else { if(obj.isBRep) { var subs = obj.getSubObjects(); for ( var j = 0; j < subs.length; ++j ) { var sub = subs.item(j); if(sub.styleIndex == si){sub.styleIndex=activstyleidx; sub.selected=true; savedobjsnum +=1; }}}}}if(savedobjsnum == 0){var selobjects = gd.getSelectedObjects(); selobjects.setProperty( "styleIndex", si ); }');