If you have a chance and willing, would you elaborate as to why the S12 would be louder than the A? The stipulation is that the S moves more air at less rpm and less dBm, unless you believe the case will be A likely working at its half or so capacity and the S going full balls.
Yes, I believe due to the air resistance inherent to all factors involved (the semi-restricting bottom plate, the short distance from the fan to the desk/table top, and the limited clearance above the fan) that the A12x25 will be more effective at moving air at lower RPM. It's also a newer design and may (i'm not 100% sure) use superior bearings and motor components. The A12x25 is simply one of, if not the quietest 120mm fans on the market at a given CFM in most situations.
I did have a desire to replace the feet, even before you mentioned it. I have read several accounts here and on Discord, where people are complaining of the stock 3M "bumpers" gradually "moving" due to the case warmth degrading the adhesive and the vibration from the PC working making the feet "slide" out of position and, frankly, fail entirely. I've been perusing some speaker/turntable feet on AliExpress - just a matter of finding the style I like. I am hoping for ~20mm diameter and ~15mm height - give or take.
My Ghost Build (seen here: https://pcpartpicker.com/b/Nvjp99 ) uses custom feet I got from amazon: https://www.amazon.com/gp/product/B075KPHZPF/
The stock adhesive is essentially worthless, but I have not seen any movement or failure of them yet. I don't move the case around much though, so there hasn't been any real risk. A drop or two of a better-suited adhesive like a Silicone-based compound would work, but bonding aluminum to rubber in general can be a challenge.
Also note that i have a 15mm thick can and custom cables, and I'm still very close to the fan blades. It's definitely a tight fit without adjusting the PSU bracket further if you went with a 25mm.
Hmm I’ve shared the link before. They’re from amazon. Just some rubber sub woofer feet. I use double sided tape to get them to stick. Hudson Hi-Fi Silicone Isolation... https://www.amazon.com/dp/B075KPHZPF?ref=ppx_pop_mob_ap_share