You are buying small custom made components, If you DIY you won't get nowhere near the size of the small cube shaped cube, temperatures either
I don't really consider temperature on my PC, unless I'm really putting it through it's paces, and then it's to make sure it DOESN'T throttle.The steam machine does the opposite, it pre-throttles to avoid overheating for... some reason, and to the end of reducing performance to barely matching the series S (so, ps4 pro/xbone x levels)