No, no, no you don't need a new CPU. You are only at 20%. You want to buy a new one and get it down to 10%? As with any performance issue, you have to address the bottleneck. Great example is when my father in law bought a new computer because he thought it would fix his problems with Skype and you tube videos. I warned hi that his real problem was that his internet connection was only .5 Mbit and the fastest computer he could buy wouldn't help. Guess what, he was disappointed in his $1,000+ purchase,
So how is your connection? Other devices simultaneously eating your band width like someone watching Netflix in another room? Are you on wireless and if so what is your signal strength? Interference from other devices on the same channel like your neighbors router? Try running a speed test.
Just saying, exhaust other possibilities before spending a lot of money on things that contradicted the underlying issue,
Well, yes and no. I've got kind of a menagerie of PCs here, and I pull different ones out every once in a while, to do updates, make certain that they're still working and booting and ready to sell, and I test them for a few hours or a day or two, browsing, etc.
I recently swapped my gigabit home wired LAN, from a Verizon gigabit internet plan, to a 15Mbit/sec plan on a different provider.
You want to know the honest truth? I can't really tell much of a difference. Ok, Windows Updates, and using the Media Creation Tool takes 2-3x as long to download. But just web-browsing, and not massive downloading, I can't really tell the difference. (Ok, don't know if I've tried 4K UHD YouTube yet on the 15Mbit/sec connection, that may or may not work OK without frameskipping.)
But for basic browsing, anything over 10Mbit/sec, is mostly more dependent on latency than overall bandwidth.
If you have less than 10Mbit/sec, or share a connection with someone that streams videos, or games, or torrents online, then I guess it could be an issue.
So, bandwidth is like RAM. Once you've got "enough", any more is just gravy and mostly unnecessary, but if you don't have enough? Thrash / lag-city.
Edit: So really, you ARE on to something, you need to identify and eliminate the bottlenecks to performance, and as you mention, it may not be the PC proper that's the issue, it may be the speed of your internet connection.