Now that I'm alternating between two daily drivers (my Quad G5 and my Talos II), the Quad G5 sleeps fairly reliably with the Sonnet USB-FireWire combo card out once I move the KVM focus off it. If I don't do that, the KVM detects the G5 has slept and moves the focus automatically away from it, which the G5 detects as USB activity, and exits sleep. The solution is a little AppleScript that waits a few seconds for me to switch the KVM and then tells the Finder to snooze. The Talos II doesn't sleep yet but I'll be interested to see if later firmware updates support that.

But sleeping the G5 has unquestionably been a good thing. Not only does it prolong its life by reducing heat (another plus in summer) as well as saving a substantial amount of energy (around 20W sleeping versus 200-250W running), but sleeping also can speed up TenFourFox. If you have lots of tabs open and those tabs are refreshing their data or otherwise running active content, then this contributes to a greater need for garbage collection and this will slow down your user experience as this overhead accumulates. (This is why running TenFourFox from a "fresh" start is much faster than when it's been chugging away for awhile.) It's possible to "pause" TenFourFox to a certain extent but the browser really isn't tested this way and may not behave properly when this is done. Sleeping the Power Mac pauses everything, so the cruft in memory that garbage collection has to clean out doesn't pile up while you're not using the machine, and everything comes back up in sync.

A whole lot of stuff has landed for TenFourFox FPR9. More about that when the beta is out, which I'm hoping to do by the middle-end of July.

http://tenfourfox.blogspot.com/2018/07/pro-tip-sleeps-good-for-your-power-mac.html