So Simon ..

The cross sectional area is approx 38 sq mm.

The flow thru a standard extinguisher valve is ( according to Jeremy ) 0.7kg/s or 70 litres ish per sec @ full pressure.

Working from the area Mario that gave ..you have an orifice equivalent to 7 mm dia .. and the flow thru a 7 mm bore pipe is 6.85 litres/sec @ 5 bar.
so ... Yes .. 68 litres/sec @ 50 bar.

A 1/2 Burkert valves give a flow approx 3.4 time better....but of course you need a supply orifice of 1/2 or bigger to realise its potential.....Hence the use of H.P.buffer tanks with large supply outlets.