there are differing opinions on whether to have the radiator exhausting into the case or out - some say it's only a few degrees difference so it's not a big concern. Personally i feel it's counterproductibe to extract heat from a CPU or a GPU into a liquid medium, then release it back into the case
I render quite a bit of video files - i had Handbrake doing a number of files, and i monitor temps while it's running, but i also employ ReatTemp as it gives me a small "widget" window displaying those temps as well as an alarm that sounds at whatever temp you set it - i set it at 85C
We maintain the house at 72F normally (i'm in Virginia, so winter is in full force). Core Temps on RealTemp were ranging 72C to 78C, with one or two cores occasionally spiking to 80C. The wife bumped the house thermostat up to 74F, and within five minutes the ReatTemp alarm was sounding - it had spiked to 85C for a long enough duration (3 seconds) to sound.
Point is, a 2F increase in ambient temp, which is also intake temp, had a magnifier effect on CPU temp (i'm still air cooled but going liquid, just waiting for some components to arrive), but a magnifier of 5C on spike temp, and 3-4C on core averages.
I've got a temp sensor built into the computer case (Aerocool DS200), with the sensor hanging down about 5" behind the air cooler, back toward the front of the case. When house thermostat is set to 72F, temp on case is showing 20-21C, when thermostat is set to 74F, it shows 22C.
THe above is also with the case cover off the left side of the case.
Get a temp sensor, XSPC has a decent one with a LCD display for about $10 (
https://www.amazon.com/XSPC-Sensor-Temperature-Display-Black/dp/B06Y5PFDLX/ref=sr_1_1_sspa?ie=UTF8&qid=1546620790&sr=8-1-spons&keywords=xspc+temperature+sensor&psc=1 ) , and monitor interior case temps with the radiator set both ways, and see what affect it has on GPU temps
Just re-read your post - and i missed the focus of your post again, i'd put the GPU's rad in the front, exhausting out - i'd also make sure you have same number of fans blowing air into the case as out. which shouldn't be a problem for that case. On mine, i'm turning what was the orig exhaust fan at the top rear, turning it around to blow in, and fabricating a small shroud to direct it's air down onto the motherboard and VRM