That seems consistent. The Eheim is obviously more efficient.
Each pump will have a different curve. Some pumps, often referred to as "high capacity" will not drop the flow rate as much, as the pressure increases. (Eheim)
All: to convert L/h to GPH, just divide the figure by 3.76 . (There are 3.76 Liters in a U.S. Gallon)
490 L/h = 130 GPH
453 L/h = 120 GPH
276 L/h = 73 GPH
370 L/h = 98 GPH
(for Eheim 1250, block and rad)
That's not bad. It's on the low side though, I would have expected 130 GPH, but if adding the two Renna's do that, then you're all set.
Also, keep in mind that the higher the flow rate, the more restriction there will be, and this is an exponential curve. As a general guideline, keep the pressure under 10 psi, where 5 to 8 is about ideal. Anything higher is not very efficient.
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