1. The Redux is an older design and is actually worse.
2. The fan needs to be at least 5mm away from the side panel to avoid turbulence. It is a very often reported concern.
3. The L9i is pretty much at maximum dissipation so a better fan does little to improve to the overall performance.
Thanks heaps for the detailed reply, I have a couple of the redux fans anyway so I will test out but I'm sure you're correct in turbulence from the proximity to the side panel. Some preliminary tests I ran were really good though, the redux is completely inaudible and I feel like with the windowed panel granting some extra space, while it may reduce airflow slightly, the extra space to the panel will reduce turbulence.
At the end of the day it is cooling an undervolted i5 8400 running at stock, so it doesn't have too difficult a job to do.
I should probably also note, while performance is important, the redux is in use because my build is a light grey/dark grey theme which it suits perfectly.
Anyone know when the windowed side panels will become available again?