Ok I tried to get dP/dQ numbers but the Omega pressure gauge is going to take a little more messing with before I feel really confident with it. So as usual not as much as I'd like was done today.
As I mentioned above, the first configuration would be considered a fairly typical one: Black Ice Extreme, Dangerden Maze4, 1/2" Clearflex tubing. When plumbed into a loop with my flowmeter and a 1gallon res, with stock barbs on the hydor and the ehime, with a 3/8" copper pipe as an inlet on the Laguna (it was modified from submerged to inline) and with a 5/8" hosebarb on the Hydrothruster's inlet, the flow rates were:
Hydor L20: 1.27 GPM
Eheim 1048: 1.32 GPM
Laguna Model 3: 1.59 GPM
Hydrothruster 500: 3.27GPM
These numbers surprise me a little because from the MFGR specs:
http://www.procooling.com/users/phaestus/pqcurves.jpg
I would have expected the L20 to have a higher flow rate than the 1048.
KE never came over so I don't have his Eheim 1250, and the Hydor L30 is being repaired right now after I ripped my pump/res off the inlet. It should all be dry now so I can take the clamps off tomorrow and test it out as well (and maybe get KE's Eheim).
The hydrothruster is in no way suitable for normal watercooling use. It's quite simply loud as hell at full blast.
I'll keep playing with my pressure gauge this week and see if I can't get the L30 and 1250 numbers for the above system and then switch to a bigger heatercore. 2 wbs, and a GPU block for a "high restriction" case as well.