[Vinnie]

Aw, I’m running 10.10.5 Yosemite and have been reluctant to upgrade. Heard Hi Sierra can really slow down an older machine.

[PIF]

I’m running 10.68 and have no intention of upgrading ever.

[Drago]

Running HS on a 2008 3,1 Mac Pro no noticeable slow downs from Yosemite days. (8 core Xenon w/SSD 16 gig RAM).

[Swordmaker]

Aw, I’m running 10.10.5 Yosemite and have been reluctant to upgrade. Heard Hi Sierra can really slow down an older machine.

Nope, not really. The first macOS High Sierra 10.13.0 had a few bugs, but macOS High Sierra 10.13.1 solved the vast majority of those. Apple upgrade first releases are seldom perfect. It takes lots of people in the wild finding those pernicious hidden bugs using lots of variations of hardware and software mixes to find all of them, even with Apple where they control the whole widget.

There are several extremely important security upgrades between Yosemite and the last iteration of High Sierra you really need. If your hardware can use High Sierra, upgrade.

[lgjhn23]

“...Aw, I’m running 10.10.5 Yosemite and have been reluctant to upgrade. Heard Hi Sierra can really slow down an older machine....”

I’m running 10.13.2 High Sierra on a mid-2010 iMac w/32gb of ram, and it hasn’t slowed this old beast down a bit. Of course, I’m not compiling mountains of raw computer code...just email, web browsing and real-time streaming market data.