I've never really done a serial loop so cant compare but with modern blocks and pumps these days loop order and layouts don't really make that much difference from what I've read and experienced my self. you could do this build with one D5 and run on level 2 without much issue but obviously use decent rads.
The Hoses are connected to the GPU with a Y rotary on the back side of the GPU.
RES> Front Rad>hose routed to the backside of case into GPU with a Y splitter to CPU out of CPU into the Y splitter which connects to the output of the GPU > back to top rad > RES
Temps are pretty much what I'd expected. CPU idle sitting nicely at 25c normal desktop use is around 30-35c never goes above 35c.
On load using aida 64 CPU stress 100% for 20mins the CPU sits comfortably at 50c VRM sits at 38c/40c - Ryzen 7 1700X @ 4.00Ghz
On my bench test (open bench) with air before it all went water cooled the CPU on 100% load would hit around 80c VRM was around 50c stock AM4 air cooler nothing fancy.
GPU 1070 OC idle - 28c / Load - 32c/35c
Fans run on PWM and don't really go above 700Rpm unless the CPU sits at 100% for 10mins which it will never do. What I don't have to hand at the minute is water temp. From my previous build water temp was around 27c iirc. Need to put a sensor on air in too or room temp.