After I saw the review of the C4-SFX on Optimumtech i needed some hours to think about it because while I liked it very much I got mixed feelings on the conclusion.

Pos:
- Could be flipped 180°
- Easier GPU installation
- Good cooling with the U9S and side mounted 140mm fan
- Sandwich layout result in very good GPU temps

Neutral
-similar to the M1 in CPU cooling for classic layout. Real advantage of 280 AIO is not present

Negative
- sandwich layout requires much higher fan speed to be as good as classic layout for CPU temps
- No bottom plate in flipped 180° use-case

Please help me with the next steps...

1.) Keep the case as it is and add a bottom plate and try to optimize airflow for the riser section.

- This will not change temperatures for classic layout
- Sandwich CPU cooling will be better

2.) Make the case 15mm more wide and drop sandwich style.
- Bigger gap between radiator and motherboard (4-5°C) better temps I tested it already
- 3090FE or 3090 STRIX support because of a bigger width
- Heatsink up to 145mm -> some 120 tower-heatsinks will fit like Cryorig H7 Plus or Thermalright AS 120min
- riser layout will be obsolete drop it
- The case will be not as slim as before and results in 13l instead of 12l.

3.) Make a pure dual chamber sandwich case with a flexible riser that fits 280 radiator and 3 Slot GPU in 12l.
- Similar CPU temps like the Meshilicious
- Good 30x0 FE temps because of the bigger gap between PSU and GPU