Hi,
At best expect half the filter rating as a realistic guide as to what you actually get but then all setups are different as previously mentioned. If you really want to know just measure it, put a Litre jug under the outflow and time how long it takes to fill. The maths is pretty simple from there on in even I can work it out.
The EI 10x guideline ruling took into account of the flow losses initially but even following that you have a shortfall of 600Litres per hour on a 180 litre tank.
I use 2 x EX1200's on a 240litre tank and have a aquamedic reactor inline on one of the returns. I've found that I needed to suppliment this with 2 Koralias adding a further 4000LPH of total flow to the tank which is around 25x tank volume. But having said this my flow pattern isn't the standard back to front commonly advised, more a left to right along the entire front face of the tank which requires a lot more flow to achieve even distribution.
I think an awfull lot depends on your flow patterns and the hardscape/flora that has to be overcome to avoid deadspots.
Regards, Chris.