Have you ever measured real water pump output flow rate?

I made a little experiment this morning in my bathroom...
I hooked up two pumps to my future sump to compare their
performance in pumping water into InstantOcean 6 1/2 g
bucket positioned in the bathtub with the upper edge
about 4 feet above the pump and my findings quite
disappointed me: neither pump showed their expected
efficiency in pumping water... How can we explain this?

Let me give you some details:

1st pump was Little Giant 3-MDQ-SC ($115) with the theoretic
maximum flow of 700gph and the flow at 4' in the range of 630.

2nd one was QuietOne 3000 ($39) with the flow a little bit weaker.

Both pumps had different fittings so I used necessary couplings
and both were pumping water through 10 feet long 3/4" ID hose
to the bucket. I have measured the time with my clock 5 times
for each pump and skiping the one value which did not match
the rest ones the most the average value was calculated.

It took average 52 seconds to fill the bucket for the Little
Giant pump and on average 69 seconds for the same task for
Quiet One pump. Taken from the measurments calculated flows
were respectively 451gph and 339gph. Why are they so low?
Can it be the lenght of the hose or couple of PCV fittings
reduced the flow so dramaticaly or the manufacturer data is
misleading in that matter?

BTW - I used my wattmeter to measure the enregy consumption
in this setup for both pumps and the Little Giant was taking
in the range of 79-82W but QuietOne only 27-31W to do almost
the same job.

QuietOne is 1/3 the price of Little Giant and consumes less
than half of the electricity to do similar job... But is has
the design of regular powerhead with resin filled electrical
engine and the magnetic rotor inside the pump. Little Giant
has this "real inline pump" design with a separate motor
and magnetic driven impeller in the separate housing.

BTW - the little giant and quiet one are very similar with
the level of noise when compared with naked ear - I do not
have any decibele meter but they seem to be same loud with
the exception that QuietOne starts in a hard way with loud
click/sound while Little Giant starts in a very soft way
accelerating rpm during first second from turning it on.

So I would have two questions to the group:
1. what could be the reason for so small flow rate measured?
(550-600gph expected, 339-451 measured)
2. which pump would you recommend for the return pump for 30g reef?