We've been here before, but Partick sees 14 an hour in each direction, meaning a total of 28 trains an hour stop at the station off peak. By comparison, Sandhills (mentioned in the OP) has a mere 16tph off peak. To make this even more impressive, there's also some empty workings, and a number of extra services in the peak hours (although a number of these go through non-stop).
Obviously this is nothing compared to current subway/underground frequencies, and nowhere near what's going to happen on TL, but I can't think of anywhere with as high a frequency over a two-track line anywhere else in the UK (although I'm willing to be corrected!). Unfortunately, the journey planners are crap for the Thameslink line (duplicating most services), but I think Partick beats it off peak at the moment.