completely depends on the chiller ira. for most chillers, 3000 litres per hour (790gph) is probably too fast. i do agree that there should be a minimum flow rate though. the flow rate should be within the minimum/maximum spec's as detailed by the chiller manufacturer. as an example, my chiller (1/2hp) has a recommended maximum flow rate of 300gph from memory. however, i have seen some chillers with maximum flow rates of up to 900gph so as i say, depends on make. see here for some general information:
http://www.marinedepot.com/aquarium_chillers_heaters_teclima_information.asp?ast=&key=