RU,
If you have to run an IntelliFlo at full speed, you just have the wrong pump. You most likely need a single speed waterfall pump..
As far as run time, I have three IntelliFlo pumps and they all run 24/7/365.. One has been running this way for over 10 years, one over 8 years and the one at my house over 7 years.. Without any issues... But then again, I run them most of the time at 1200 RPM and you can't hear them.. An IntelliFlo at full speed is a screamer..
If you run your waterfall 24/7 your main problem will not be the pump, but the fact that your pH will increase drastically..
Thanks,
Jim R.