I've a 7th i7-7700K at 4.2GHz and the motherboard is going out. I'm trying to sort out if I should replace the CPU as well and just rebuild using the new 10th gen stuff, but am very unclear if it's worth the $$. Would it be better to replace with a 9th gen? I haven't kept up with CPUs in a bit so I'm struggling on finding benchmarks and whatnot.. any guidance is very appreciated. I am sticking with Intel.. just personal preference
"games and for work graphic creation"
In Photoshop and DaVinci Resolve Studio benchmarks, the 7700K is about on par with a Ryzen 3100.
In gaming, the 7700K is about on par with a Ryzen 3300X at 1080p.
Ref:
Techspot
For $75-100 you can just replace the motherboard and just keep trucking along, until the release of Zen3 drops Zen2 prices or makes a full upgrade to the latest tech compelling.
The Intel 10th gen stuff is probably not worth the cost premium right now.
If you can even get one of them. A 10400 on a cheaper motherboard will be locked to RAM speeds of 2666 and at that speed it's basically the same as the 7700K from a gaming standpoint, basically the same in Photoshop, and within 15% in Resolve Studio. Though in Blender, the 10400 is fairly decently ahead. (I am NOT saying it's equivalent in all tests, but just from an overview of the Techspot benchmarks, it's not a significant difference.)
IMO, a 10400 would be a side-grade and a wasted $160.
Now, a 10600 might be more compelling, but it runs $265 and yet is about on par with a $159 Ryzen 3600 or $199 Ryzen 3600X in productivity apps, but the 3600 and 3600X are within 10% in gaming. And really to maximize the 10600 you need one of the nicer $175-200 new LGA1200 mobos that unlocks faster RAM, you'd probably need to buy faster RAM to exploit that, plus you'll need a cooler too, so the total out of pocket cost for the 10600 would be ~$265 + $185 + $30 + whatever the net cost of selling old RAM/buying new RAM = $480+. For that price you can snag a quality MSI B450 Tomahawk MAX ($115) plus a 3700X ($275) and 2x8GB 3600 CL16 RAM ($85) = $475. The Ryzen system would be at least 8% faster than the 10600K in productivity apps, and less than 7% slower in gaming at 1080p, and within 3% in gaming at 1400p.
Right now Intel is keeping up, but only just so, and still, unless you have specific apps that would benefit from Intel over AMD to justify cost increases, doesn't make sense.
IMO, stay put and grab a new mobo for your 7700K and watch how things unfold.