It’s bit humbling to ask this, but can I connect two PCs each with a 10GBASE-T connector directly using a Cat 6A cable or do I need a switch? (or, heaven forbid, some sort of special cable – I still remember cross-over cables).
yes
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Thanks! I figured as much, but didn’t want to let my pride get in the way and maybe mess something up.
As long as the PCs are within 100m of each other 
And it’s plug and play. Crossover cables are a relic of the 20th century.
You can even connect 3 PCs by using two ports on one PC. You can get very creative if you want to avoid buying expensive switches (and 10GBase-T are expensive)
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As am I. 
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So if you connect two pc’s to each other and then connect one of them to the network will they both have internet access or will that require configuring?
needs some software routing for that subnet and some bridge between the networks (like the bridge your VMs use to get internet). But you can link up as much machines as you want. But port count increases rapidly, and daisy-chaining eventually gets slower and slower because multiple hops and if one goes down, network goes down. It’s basically back to the 90s with bus topology, BNC cables and terminators
But for like 3-5 machines and a bunch of NICs, you can do without a switch.
I played around with frr before I got my 10Gbit switch. I consider using it again when I get my 25Gbit stuff.
Mellanox ConnectX-5 has built-in capability to do this and they claim better latency and less CPU overhead. But for the price on ConnectX-5, I may as well get X-4 and a switch 
Cool, i’ve got some connectx-3s i want to direct attach between 2 devices so i have a 40g connection to my nas and my switch sounds like a jet engine so i can’t bring that to college lol. I’ll have to look into the subnetting bit