Well, I tested my theory while away from an internet connection, and it seems the number of pumps required to get a constant flow of 7/7 water for one pump when fed from an aquifer is just too fucking large. I got up to 54 pumps feeding one from two troughs cut in the aquifer, and still got an inconsistent flow out of the top.
However, I scrapped all of it, and rebuilt a similar design next to it, only adapted to work as a repeater. Four sets of four pumps each feed another pump on the level above to produce a constant set of 7/7 water for another pump to draw off of, so long as it doesn't run long enough to drain the lower reservoirs. The repeater at the top is... hmm. A pump feeding a one tile reservoir with a pressure plate attached to a gear to turn on another pump that drains that square into a five tile reservoir, with a pressure plate set to 0-5 at the start and a drawbridge next to the other four squares. That pressure plate links to the drawbridge and a gear that controls the first of these pumps. I think the first pressure plate is superfluous, but I'm not sure. It seems the top pump always runs, and that reservoir is only empty for one click anyways. I'd try to make a little ascii graph of it, but I can neither make nor make sense of those...
It *looks* like it runs at a constant interval, and it should, logically. But when I built it my mind was too foggy to count right. I built it this afternoon based on designs I came up with in the morning, but was too tired to understand while working with them, I even screwed up the top pressure plate the first time around, and had to destroy it and the bridge and redo all of that. Every part linked to a pressure plate was also linked to a lever, allowing fiddling around until it starts working right.
Hmm... just tried counting cycles, and I got 114 from when the bridge has closed to when it opens again :/ . I'm thinking there's a bit of randomness introduced by water draining off the pad. Or something like that. Or I'm counting wrong. Well, I'll see if I can't figure this out... The down tick seems to be a perfect 100, though it should be 101, shouldn't it?
Edit: Yeah, it's a delay while water leaves the pad. A 7/7 column of water just stands on it, so it doesn't get triggered for ~10 cycles. :/ Need to make a design that alternates between two repeaters then. Or something like that.