Help Choosing a Pre-built Gaming PC Please

So I have a pretty bitchin’ videocard. It’s an RTX3070. And it’s been slumming it in my computer from 2014 for far too long. In fact, the videocard is actively trying to murder the rest of my computer: my venerable Intel i7-4790 is hitting the limits for CPU loads and the cores’ temperatures are getting silly hot, to the point that it was causing shutdowns. Replacing the thermal paste has bought me some time, but the writing is on the wall: This isn’t enough computer for this much videocard!

So I need a new rig, not including GPU. My current computer was from Maingear, but I don’t have any particular allegiance to shopping with them. @mono found a seller local to me with a variety of options. I’ve reached out to him, but haven’t heard back yet. He seems to have access to an insane number of barebones systems that I can’t really make heads nor tails of. I’m left comparing various CPU and motherboards, which mean bupkis to me.

I just want something fast and capable of keeping cool after I drop in my RTX3070. I’m okay with paying more for something that will hopefully last another eight years. Although I wouldn’t mind saving a few bucks on some quick n’ dirty exchange with someone local, I’d be more comfortable buying from an established online outlet.

So can you guys point me to someplace good for a pre-built system into which I can drop my GPU and hard drives? And more importantly, can someone just tell me the best CPU to get these days that doesn’t cost sillymoney? Mobo recommendations would also be welcome.

-Tom