Love those HK blocks...

I think flow is as important as it ever was, i mean there is the optimal flow rates to cool your system based on
ur components. If it's slower or faster, there always is a sweet spot...

Plus the OP is using a killer pump / radiator set up, so his temps should be very nice
using a 480 and Typhoons.

but I think that as you would drop his flow, he better have a big honking rad on there
because the flow thru the gpu's goes down by 3. and when it starts getting to slow
then it will easily start to heat up.

Say he only had 1 GPM that is .33 for the cards,
or even .75GPM takes it down to .25GPM per gpu

So i would think that with parallel cooling the flow matters even more then in series.

keep the numbers coming, sweet work.