What CPU can I get away with?

I’m looking into putting together a SFF living room PC at some point for 4K/60 gaming. Intending to play some AAA stuff, high/ultra settings, assuming the 5070ti will be able to handle this with DLSS and/or frame gen (I know there’s no benchmarks yet, but let’s assume 4080 performance, give or take).

The question is what CPU can I get away with? Would something a little older suffice? For example, would a 5600x3d do and offer a reasonable amount of future proofing, or should I be looking into something a bit newer?

Also, with it being SFF (looking at the Fractal Ridge) thermals are something I’ll need to consider too.