Ssd not hdd. Ssd is around 5x faster than a decent hard drive.
Ram size depends on usage. If you are continuously running up close or over 8Gb, then a move to 16Gb makes sense. You won't use all of it, but it's far better to have and not need, than need and not have. With ram, if you need it and it's not there, it uses pagefile to portion part of storage as temporary ram, and thats slower than moving molasses in Siberia.
As for performance, that starts in Windows. Turn off things in Startup you don't need or use much at all. Run through your apps, look for things you really don't ever use, and see if they are set to self start with windows, bypassing startup. I use a small program called WinAero to change Windows settings, turn off the Store, live feeds, tiles, Cortana Voice etc, all the stuff that's not readily available options for disable.
Streamline the garbage and there's less need for cpu processes.
Usage is somewhat confusing. Usage isn't how much of the cpu/gpu is used, it's how much resources they are using vs the time not using anything. You don't ever want to see 100% usage, or that means the cpu can handle no more, has no time for anything extra. So if you were at 100% walking through town, and then a wall exploded, all those extra instructions and computations of all the vectors of the chunks of wall would have to wait their turn. Fps would tank and hard. No extra room to think. Performance in the toilet.
Same applies to the gpu. It'll only use whatever resources it needs to use per frame, and no more. You want a smaller %. Thereby allowing the gpu room to add complexity when it needs to, without tanking the fps.
Think of it like putting a nail into a wall to hang a picture. You use a small hammer, not a 2 handed sledge hammer. You will use 100% of the muscles in your arm to hold the hammer and swing it, but you won't use 100% of the Muscle, All your strength. It's not necessary or warranted. But if you hit a stud in that wall, you have the extra to hit the nail a little harder, use more strength to swing the hammer if needed, and not slow your swing.