Hi Planetq,
I'm currently with a 6540, supposlingly running on 100 watts with a 2880 l/hr output....
If you need to test run it to see whether it gives a better flow output, pls PM me ....
You might also wanna consider your pipe work again..... every PVC elbow instlled into the pipework brings down the flow rate by a tremendous lot....
have you consider using flexible tubing instead.....?????