Requirements to make Windows 10 feel smooth?

Hi Plecto, welcome to the forum.
What you are asking is pretty individual thing. I find anything with less than than older (4th generation processor), 2 cores, up to 2.5 GHz, 4GB of RAM and slow HDD pretty unbearable even for simplest tasks. It may be just enough for some business and very simple games but that's about it.
That goes for any computer with above Windows XP. If you have right drivers, W10 should be at least a bit faster than Vista and up.
SSD makes some difference in overall feel of course but except for faster BOOT and programs start they don't do anything for programs themselves.
I could say that having enough memory can make most difference. Less than 4 BG of RAM makes it swap to virtual memory on the disk and if that one is slow look out, molasses may look like fast river !

Plecto said:

Thanks for the replies :) Lets say the the computer in question is just going to be used for playing music, comparing my life to other people lives on facebook, and mine sweeper. None of these programs require a fast CPU and having 4GB (perhaps 2GB is enough?) of RAM should be enough to do all three at the same time, the smoothness-feeling then boils down the the bandwidth of the hard drive, the time it takes for the programs to load from the drive to the RAM?

Those things would run just as well on a phone with much less performance but that would not make windows on desktop look any faster.
Mine sweeper was made at the time of 386 DX computers and is not going to look and work any different on a top end server. Facebook, except for some badly optimized games on it, can also be used on practically any configuration but open 5 tabs in Chrome and it will eat all of 2GB RAM and practically work of the HDD and swap file slowing it to a crawl.

In short, yes. It isn't so much the age/generation of the processor as much as it is the quality of it. For the first year or so I ran windows 10 I was using an i7-875k. Ran like butter even though that is an "old" chip. In fact the only reasons I upgraded were 1.) I got a 50$ i5-4570 that was essentially brand new and 2.) I needed a processor with a higher STP for emulation. But just for videos/music/browsing older chips are fine. If it was mid to high end when it was released chances are it will run fine now. If it was garbage then it certainly won't be magically fixed by a new OS :P

Out of curiosity what was the old cpu you were trying to use before the pentium g3250?