Windows 10 is the newest OS and it's more suitable for newer hardware, mainstream support ended in 2018 for Windows 8.1, so you will not receive any security updates, otherwise if you are happy and more familiar with the way 8.1 works you can continue to use 8.1, the boot time depends on the...
You could try disabling Power saving feature in Power management tab(Device Manager) by untick "Allow the computer to turn off........) and switching DNS to either google dns or Open dns also may be helpful.
How to change the DNS settings on the Dlink DSL-3680
I have v7.0.5 (Win 8) in my Win 8.1, you could try different versions from here:Download Drivers and Manuals | Acer Official Site
One of them will work for you, it doesn't show in start up for me as well.