The very slow Double that the HSQ replaced at Burke actually had almost the same capacity as the HSQ. THe double had chairs very close together and the HSQ has them a mile apart. Result = very fast ride to the unload area but a bit of a line now forms on busy days. To be fair the old double hardly ever ran a optimal line speed since it was hard for little kids to get on as the chairs whipped around the bullwheel. This led to A LOT of stopages.
There are definitely cases where an HS lift might actually have a lesser capacity than an FG lift. There are also cases where the capacity is higher, such as replacing a slow wide-chair spacing FG quad with a new HS quad with average HS chair spacing. It all depends on the situation. But the general rule is this: Ropetow > 300pph; Poma 600pph; T-Bar > 1200pph; Double 1200pph; Triple 1800pph; Quad 2400pph.
Of course, you can get variations all across the spectrum. I've seen quads with a capacity of upwards of 3000pph, and I've seen them with > 1800pph. But for reference in a discussion like this, you follow the general rule above.