bad performance with scaled QPainter and drawing QPainterPath

#include <QtGui/QApplication> 

#include <QGraphicsView> 
#include <QGraphicsScene> 
#include <QVBoxLayout> 
#include <QTime> 

class MyGV : public QGraphicsView { 

public: 
MyGV(QWidget* parent=0) : QGraphicsView(parent), mDrawCnt(0) { mStartT.start(); } 

protected: 
void paintEvent(QPaintEvent* event) { 
QGraphicsView::paintEvent(event); 

/// trigger another repaint 
viewport()->update(); 
} 

void drawForeground(QPainter* painter, const QRectF& rect) { 
painter->setTransform(QTransform(),false); 
painter->drawText(10,10,QString::number(++mDrawCnt *1000/mStartT.elapsed())); 
} 
private: 
int mDrawCnt; 
QTime mStartT; 
}; 

#include <QGradient> 
int main(int argc, char *argv[]) 
{ 
QApplication a(argc, argv); 

QGraphicsScene* scene = new QGraphicsScene; 

const QRectF testItemRect(-100,-100,200,200); 
#if 0 /// performance issue doesn't happen with simple Rects 
scene->addRect(testItemRect,QPen(Qt::red), Qt::green); 
#else 
const int EDGE = 10; 
QPainterPath path; 
path.moveTo (testItemRect.bottomLeft() - QPointF(0, EDGE)); 
path.arcTo ( QRectF(testItemRect.topLeft(), 
QSizeF( EDGE*2, EDGE*2)), 180, -90); 
path.arcTo ( QRectF(testItemRect.topRight(), 
QSizeF( -EDGE*2, EDGE*2)), 90, 90); 
path.arcTo ( QRectF(testItemRect.bottomRight(), 
QSizeF( -EDGE*2, -EDGE*2)), 180, -90); 
path.arcTo ( QRectF(testItemRect.bottomLeft(), 
QSizeF( EDGE*2, -EDGE*2)), 90, 90); 
scene->addPath(path,QPen(Qt::red), Qt::green); 
#endif 

QWidget mainWidget; 
mainWidget.resize(200,200); 
QVBoxLayout* layout = new QVBoxLayout(&mainWidget); 

MyGV* view = new MyGV; 
QMatrix matrix = view->matrix(); 

/// 10000 -> ~27 fps 
/// 1000 -> ~85 fps 
/// 100 -> ~1900 fps 
/// 10 -> ~2200 fps 
/// 1 -> ~2400 fps 
/// 0.1 -> ~3000 fps // a lot of white space 
const double scaleValue = 10000; 

matrix.scale(scaleValue,scaleValue); 
view->setMatrix(matrix); 
view->setScene(scene); 
layout->addWidget(view); 

mainWidget.show(); 

return a.exec(); 
}