The problem with the workhorse ballasts is that they are instant start ballasts. Fulham will give you the wiring diagrams to run t5HO bulbs with them, but they do not run the bulbs to the t5 specs. T5 ballasts should be a programed start, not an instant start. So yes they are not the best, but they will work. Or sell off your PFO ballasts and get some good real T5 ballasts, might even make money in the trade...
Kim