Based on my testing of a 400W FSP unit, I'm pretty comfortable with the fan noise. That particular unit had a coil whine issue under load, though, which was far more annoying than the fan was.
The design as it is now likely wouldn't work that well with a short card, due to the limited space between the GPU and the back of the motherboard (9~10mm), so a blower card is probably the ideal.
Here's some trivia for you: those Shuttles use a proprietary PSU form factor that's around 10mm thicker than flex/1U, and uses a 50mm fan instead of 40mm.
The case currently isn't deep or wide enough to support an SFX PSU in the front. See my comment above on short GPUs.
/snip
@Necere, thanks for the detailed reply; I didn't know that the Shuttle PSUs were proprietary.
Coil whine doesn't make for a happy setup, I hope that a better Flex ATX PSU is available for the Sidearm as & when
I would be happy with a GTX 970 with the right blower cooler, the GTX
660 I have has been fine, especially with headphones on for gaming. Annoyingly, I just missed an EVGA GTX 970 blower, but I'm sure that there are others out there (the vast majority are, understandably, ACX cooler models).
I forgot to say that I did really like the silver case with black end plates colour scheme, it looked very smart & understated. I see that
@Lone offered the opposite colour scheme on his latest L4 batch, which looks really good too...
Happy developng! You have a lot on your plate, with 3 potential designs on the go.
BTW I have historically not liked big ATX cases - last one I had was 10 years ago (Antec 300), but something like your proposed 24L compact would have swayed my opinion strongly, as it really is small and efficient.