pyqtgraph performance

#!/usr/bin/python
# -*- coding: utf-8 -*-
"""
Update a simple plot as rapidly as possible to measure speed.
"""

## Add path to library (just for examples; you do not need this)
import initExample


from pyqtgraph.Qt import QtGui, QtCore
import numpy as np
import pyqtgraph as pg
from pyqtgraph.ptime import time
app = QtGui.QApplication([])

p = pg.plot()
p.setWindowTitle('pyqtgraph example: PlotSpeedTest')
p.setRange(QtCore.QRectF(0, -10, 5000, 20))
p.setLabel('bottom', 'Index', units='B')
#curve = p.plot(pen=pg.mkPen(color='b', width=1))
curve = p.plot(pen=pg.mkPen(color='b', width=2))

#curve.setFillBrush((0, 0, 100, 100))
#curve.setFillLevel(0)

#lr = pg.LinearRegionItem([100, 4900])
#p.addItem(lr)

data = np.random.normal(size=(50,5000))
ptr = 0
lastTime = time()
fps = None
def update():
    global curve, data, ptr, p, lastTime, fps
    curve.setData(data[ptr%10])
    ptr += 1
    now = time()
    dt = now - lastTime
    lastTime = now
    if fps is None:
        fps = 1.0/dt
    else:
        s = np.clip(dt*3., 0, 1)
        fps = fps * (1-s) + (1.0/dt) * s
    p.setTitle('%0.2f fps' % fps)
    app.processEvents()  ## force complete redraw for every plot
timer = QtCore.QTimer()
timer.timeout.connect(update)
timer.start(0)



## Start Qt event loop unless running in interactive mode.
if __name__ == '__main__':
    import sys
    if (sys.flags.interactive != 1) or not hasattr(QtCore, 'PYQT_VERSION'):
        QtGui.QApplication.instance().exec_()

With width>1 performance drops by more than 2 orders of magnitude.