The 1700X/1800X should be better binned so that they should run at the same clockspeeds at a lower power consumption.
The 1700's lower power consumption comes from it having lower clockspeeds. (stock)
There have also been reports that the memory controller on many 1700s does not seem to be as robust as the 1700X/1800X and may not be as good at handling faster memory speeds.
Temperature comparisons are skewed because the X CPUs have up to a 20C temperature offset for some reason.
My 1700X at 3.9GHz reports "73C" running Intel Burn Test (maximum heat/stress) which would be about equal to the 1700 results you've quoted, when you factor in the offset. (53C)
The motherboard size shouldn't affect this.
Trying to use an air cooler on an 8-core CPU in a cramped mITX build might cause you to run into thermal throttling though - but it can be done. A lot of that depends on the case/cooler.
Linus Tech Tips put a 145W Xeon into one of the smallest PC cases there are, and used an air cooler for it.
The current Ryzen processors are only CPUs, not APUs. They don't have an integrated GPU.
Basically, AMD put another 4 CPU cores in place of an iGPU.
More than half the chip in Intel's quad-core CPUs is the iGPU now.
Resolution in games is 99% determined by your GPU. The CPU affects minimum framerates more than anything else.
So you need a really fast CPU if you want to keep minimum framerates above 120 FPS, less-fast for 60 FPS, and even less for 30 FPS - which is why console games are mostly 30.
Since higher resolutions are going to run at lower framerates anyway due to the GPU, the CPU matters a lot less for 4K60 than if you were trying to run a game at 1080p240.
It's not a
bad CPU for gaming by any means, just not necessarily the
best across all games - though it can often be second or third on the list.
Its performance in many non-gaming applications can make up for that though, depending on your requirements. It can be twice as fast as a 7700K in some applications.
And even where it's not the best, it's still been a significant upgrade from my i5-2500K in all cases.
Check that the programs you want to run can actually use 8 cores though.
Nearly all of Adobe's programs other than Premiere will not benefit from more than 4. The same could be true of CAD programs.
A lot of these programs would probably benefit greatly if they
were well multithreaded, but the codebase is so old that it would be a massive undertaking.