A big factor in determining block performance is knowing how restrictive it is. Knowing how restrictive it is, as well as pump performance and how restrictive the other components in you loop are, you can know what flowrate to expect. Generally speaking, you don’t want flowrate to go too low–every component performs better with higher flowrates (but to varying degrees). Ultimately though, higher restriction is fine because it’s what you do with the flowrate that’s most important–flowrate is a means to get lower temperatures but flowrate without context is pretty meaningless.
Of note, “Restrictiveness” is a unitless metric measuring restriction and is effectively, not literally, an inverse of measured flowrate–lower means less restrictive. It’s a sum of pressure drop readings at the eight lowest pump settings we test.
Swiftech Apogee XT rev2 is a medium-high restriction block, so flowrate can be a concern if paired with other restrictive components or a low power pump. With the alternate inlet, it’s a high restriction block, making flowrate a small concern if paired with other restrictive components or a low power pump.
Interestingly, the Apogee XT rev2 has slightly different pressure drop curve when mounted to a CPU block than when just sitting in the open. This seems to be a trend with micropin blocks (likely due to weaker bases, structurally). All pressure drop and charted flowrate numbers are from moderate pressure mounts (either with Indigo Xtreme or as if it were with Indigo Xtreme [alt inlet configuration was not tested with IX]). Also of note, flowrate readings declined as testing progressed due to minor clogging. Block was flushed before switching to the alternate inlet configuration.
I expected the rev2 to be less restrictive than this. Swiftech says the block is half as restrictive as the original Apogee XT (and their numbers show it is), but I don’t remember the Apogee XT being that restrictive. I’m testing the Apogee XTL in a couple weeks and will be able to pressure drop test all the various Apogee XTs I have (old, new, XTL, and rev2).