its not so much that they suffered, since it is the same system as on a 930F. its just that it isn't as easy as on a 60 series.
we demoed a 9760 with a 635 to a customer that was running a 9750 with a 930, after he bought the 635 for his 9750 it took some time, more tweeking of drop rate and the control valve, and we had to adjust a few addresses to get it to not hunt, now that i think about it, that customer had a third cylinder under the feeder house, making oil control a little different, which would explain the difficulties that we had. but usually once you have it set, it should be fine for a long time.
i would strongly recomend to anyone interested to move up to a 600 series
but to answer your question, the hyraflex worked perfectly, and operation of the it is exactly the same as on a 60 series. it is a pretty simple system, we have many customers with 9600's running 630F heads
We did the conversion to run 630F on our 9750. No problems and was well worth it.
One of the territory reps said you were better to have a 600 series on a 50 series than to have a 60 series and still be using the 900 series flex. You could argue either way, but I would agree after using the 900 series and moving to 600 series with the same combine.