PS windows 10 64 bit does take advantage of quad core processor... So I'm told lol.
I big believer the reason computers seem fast when they are new is because as time and heat take effect the circuitry
Cooks and slows down.....
Yeah Win10 is a multi-threaded OS. So as long as the software you're running is written in a platform that can do worker threads, and they actually bothered to write the software to make use of worker threads... then yeah... you're squeezing the most out of a multi-core processor. (Also for apps that make use of databases, they benefit from those calls getting handled by a dedicated SQL server machine/cluster that's setup nice and stout, but you as a single person running stuff that only you are hitting against would never notice any appreciable gain/difference)
Setups slow down over time usually because of mundane things like a buncha unneeded stuff that gets left behind from prior software installs and is still running in the background and ya might not now it. Or the Windows Registry file getting big and unruly and taking lil bits of time longer to find RegKey values in there that you need to read-in in your software's coding. Or maybe the need for a little defrag'ing. (But that is less and less because now by default they can have a defrag auto kicking-off during off-peak times of the day, which is pretty freakin' cool).
Another big thing that people forget about is all the dust that gets in there and clogs up cooling fins on CPU and Video GPU's greatly reducing their ability to radiate out that heat, so many of them are smarter these days and will throttle themselves down a bit when presented with approaching an over-heating condition. Again, very cool, rather than that chip just killing itself by burning up from running too hot.
Also... I feel certain that Internet Service Providers are often, unbeknownst to the end users, electing to throttle-down broad swaths of non-business users connections bandwidth sometimes. Like, I'll notice enough of a dip in performance then what it should be and sometimes I'll call in and ask them to reboot my connection thread... which nowadays they can do while they are on the phone with you. And low and behold, Oh gee, imagine that... performance magically seems to pick back up to more what you're used to!
I can't prove that it's a deliberate action on their part. And it doesn't happen too darn often. But for me, another thing I'll do when I notice sluggish connections speeds is I might actually elect to power-down my machine for a night... then when the fam leaves in the morning, hard-cut the power to the Fiber-Optic Modem... let it get back on... then power-on my machine, so I know it'll be a brand new connection/ip-registration with their servers, and you usually notice the speed become more like what you remember then.
For you with some AutoCAD software, being setup with a beefy video card, and beefy RAM will be of significance importance for performance. That's assuming it's a locally installed piece of software.
For the most part, I try not to turn-off machines I'll be running daily. The Brown-out that happens everytime you turn-off and turn-on your machine is probably the hardest stress conditions, in the physical realm, on the hardware of the system.
not to mention our server farm can handle all the duck posts you guys can throw at us 
