After much planning and deliberating, I finally joined the club and bought myself a P360 with an i9-12900, the plan being to create a firewall capable of pushing a lot of packets! I plan to share my progress here over the coming weeks so that others might be able to benefit from my trial and error.
Photos 1+2 show that with the speaker and Bluetooth antenna removed, there is around 172mm length of clearance for PCI-E cards. It is not the full length of the motherboard as the top case assembly encroaches a little when fitted (hence the gap at the front). But that could be modded as well if you really needed to.
Photo 3 shows my NIC of choice, the Supermicro AOC-STG-i4s, the 4 port version of the popular AOC-STG-i2s. I needed at least 3x SFP+ ports and so I decided to try this out and mod away any heat issues.
Photo 4 suggests (unsurprisingly) that I may have heat issues, as the heatsink on the NIC reaches 55ºC while idle. This is the maximum operating temperature for the Intel X710 chipset, although a Supermicro representative claimed the maximum operating temperature for the card was much higher.
Photo 5 shows some research into creating a cooling solution. The AOC-STG-i4s has a "Thermal Alert Connector" header which I was curious about, although there was little to no information in the Supermicro manual. It turns out that the header itself is a Molex "picoblade" part number 53047-0310 which mates to part number 51021-0300. It runs of 3.3v logic from the Nuvoton chipset onboard supplying voltage between the centre and outer pins when the card is below its maximum temperature threshold, and voltage disappears above the threshold. Unfortunately it turns out that the threshold is 115ºC which is too high for me, so I will have to find another option.
More experiments, details and photos to come!