Hi .4,
I'm familiar with the UK rules (ex-MAN) and the rules are different here. The departure must be past the localiser before the arrival reaches the FAF (4d-ish) hence the larger spacing requirement. Its a Transport Canada rule and we tried to get it reduced citing the UK as a precedent but were unsuccessful.
Low viz ops are rare here and its only recently that we've got the second Cat3 arrival runway. The Cat3 holds are a long, long way back too which makes dual Cat3 ops very slow. Also ground becomes a nightmare since we do the crossovers on the ground. Departures from the southeast end of the airport departing to the north or west, will need to taxy to 05 which is over 4 miles, in low viz!!! Not recommended. Land one depart one means one departure line and one arrival line. Much easier.
Normally departures are issued their runway based on direction of flight so there are no crossovers. We do permit non-conforming departures on an opportunity basis. Side by side departures are stopped at 3000 and Departure decides how to do the crossover. Jet Sids are basically all straight ahead (10 degree divergence since our runways are 2 miles apart) and we have to provide departure 3 miles in trail for similar types. We turn all props.
DC