That photo of the restrictor reminds me of what they used to do 30-40 years ago with racing engines. Bet they don't do that any more. I've raced A series engines for more than 20 years (started in 1988) & not once has an engine builder, machinist or any competitior suggested doing this. I've always run a 62 degrees celsius thermostat as against the standard 72 degree one, mainly to get the thermostat open earlier. The opening in the thermostat is smaller than the outlet anyway, so the larger housing shouldn't be an advantage.