Howdy. I've gotten great pointers and tips from posters all over the vMix forums, so wanted to post a build that has worked well for me (so far) in the hopes it will help someone who is building their own, and is looking for what others have done.

The desire was to replace an older ATEM switcher plus encoder, with a vMix only PC system, using 5 SDI connected PTZ cams, HDMI feed from projection computer, to feed in-building CCTV distro in addition to vMix's encoder to YouTube.

Build included:
ASUS ProArt Z790-Creator mobo;
ASUS Dual GeForce RTX™ 4070 White OC Edition 12GB GDDR6X (PCIe 4.0, 12GB)
Intel Core i9-14900F;
ASUS ROG Strix LC II 280 liquid CPU cooler(AIO);
CORSAIR Dominator Titanium RGB DDR5 RAM 32GB (2x16GB) DDR5 6000MHz CL30;
SAMSUNG 990 PRO SSD 1TB PCIe 4.0 M.2 2280;
Seasonic FOCUS PX-850;
SilverStone Technology FARA 512Z High Airflow ATX Mid-Tower;
Blackmagic Decklink Quad 2 8 SDI I/O;
Windоws 11 Pro.

More experienced builders may see a more optimal configuration, but this has been working in a balcony that was in 90+ degree heat during the summer. GPU memory use hovers around 10%, and GPU & CPU are single digits while switching and encoding.

Outputs include 3 connections to the GPU (PGM to HDMI splitter, Multiview, and system monitor). One Magewell HDMI to USB for the HDMI feed from the projection computer.

Only issue was using a driver from BMD that made the Decklink super unhappy ("what PCIe card? I see no card here."), so backed up to v12.9 instead of v14.1. PTZ control is by PTZOptics' SuperJoy controller and switched via Stream Deck and Bitfocus Companion that also talks to the joystick for selection (select camera in preview, and joystick controller selects same for operator).