It happens to be an extremely hot day here in the uk aswell. 30 Degrees and up.
Does not affect load thermals as much as it does idle. The air inside the chassis will always be warmer than in your room.
Case: Corsair Obsidian 500D SE
A)H150i Pro is front or top mounted? Intake or exhaust? Push only, pull only, or push-pull?
The H150i Pro is a silence focused CLC that does not deliver in the performance area. If you have it set up in the front as intake, I'd suggest moving it to the top as exhaust.
B)The stock LL120s - if you're still using them - are weak, considering the gpu. The bottom and center fans likely do not bring in enough air to keep the gpu fed.
What I would suggest:
A)Front intake: Stronger intake fans are needed. I'd imagine you would want to stick with LED fans in the front...
There is a 2200rpm version of the LL120s preinstalled with the chassis.;
the SKU is different. The downsides are that the fan frames come in white only, and that they are louder due to the higher rpm.
Another alternative is the HD140 RGB 2-pack:
https://pcpartpicker.com/product/VhX2FT/corsair-hd140-rgb-74-cfm-140-mm-fans-2-pack-co-9050069-ww
That's pretty much it without having to change brands.
B)Top exhaust: The H150i Pro, with fans pushing air out of the chassis.
C)Rear exhaust: Take one of the old LL120s and use it here