Hi,

4K30p or 4K60p?

for 4K60p with decklink quad hdmi

No Gigabyte Z790 AORUS MASTER = no second pcie x8 slot

if just 2 cams, personally I'd go for :

a cheaper motherboard
slot pcie 1 x8 = graphics card
slot pcie 2 x8 = Blackmagic Design DeckLink Quad HDMI

E-ATX = ASRock Z790 Taichi (also Lite)
in ATX = ASUS ProArt Z790-CREATOR WIFI

i9-13900k or i7-14700K if much cheaper than 14900
minimal performance difference

2 x M.2 2 TB, 1 for system and 1 for rec

and put the savings into 2 x 32 DDR5 and RTX 4080

so that, if necessary, you can upgrade to more cams via decklink quad hdmi and thunderbolt ports.

the difference counts a lot, not the same needs
for 4K30, a pcie x4 card like the elgato cam link pro provides 4 in 4K30p

for just 2 in 4K30p, a powerful laptop may suffice
via 2 usb 3.0 ports via elgato cam 4k
or
via thunderbolt 4 port with Thunderbolt 3 PCIe Expansion Chassis and 2 x decklink mini recorder 4k or 1 x elgato cam link pro
or 2 x Elgato Game Capture 4K60 Pro MK.2 (for 4K60p)

in pcie x4 = Yuan SC710N2-L HDMI2.0 = 2 in hdmi 4K60p

on a pcie x8 slot the graphics card will be a bit limited but will still run well

you can start with x299
this socket's cpu can handle 48 pcie lanes, so no problem for several quad hdmi cards, but it's a bit excessive for just 2 in 4k30p

3000 cards are also pcie 4.0 x16
so the graphics card (3000 or 4000) will be a bit limited... but that's negligible

here are the results of a test performed on an rtx 3080 (pcie 4.0 x16) on different gen pcie slots

perf 3080- pcie.jpg (145kb) downloaded 2 time(s).