I’ve been experiencing performance problems (slowdowns) lately. It’s almost impossible to tell how fast and well the game is handling the data at a given moment, or if the next reading session is going to be a crawlfest. But if you’re driving, and if there are portions on the road where the car just seems to go faster, i.e. framerate goes up, make a note of it. All I know is that certain spots in the game are really fast to process, while in other places the time progress can slow down to a crawl. I hope this helps!
NPC companion autopickup
This seems to create some or heavy slowdown. Turning it off, especially for crafting, sleeping or reading, should make said operations faster, or at least not-slow. Luckily it’s disabled by default.
This is where the game is likely to operate the fastest. Find an evac shelter and go downstairs to do your reading/sleeping etc. Unfortunately you’ll need lighting. Time flies when there’s no creatures to process. Of course there could be an ant nest nearby, or zombies in the cellars of the nearby houses. Next best thing: LMOE shelter. They are likely remote.
Not sure about this one as I’ve never played with Z-levels enabled. I just suspect that enabling the 3D might slow the game in many areas. Enlighten me.
Lots of monsters nearby
Probably obvious. Do your reading and such in the middle of nowhere, preferrably in the plains. Try killing stray dogs and other nearby critters.
Lots of items nearby
If you’re like me and like to haul all your possessions everywhere in your car, then that might be one culprit. My early games are visibly more responsive than the advanced games. Currently I suspect that a lot of books in your car can slow down the game. Try tossing away some items or leave your books elsewhere. A ton of (perishable) food around might cause processing slowdown too. Or if you just killed a ton of zombies and their items litter the ground, don’t stick around to do crafting and such. Just something to keep an eye out for. I suspect clothing that’s been left outdoors now rots (loses condition), and if that’s true, then that is one possibile culprit as they’re being processed. Pure speculation, of course. Devs are crafty and sneaky. Tricksy little devsies.
Another possibility. I’ve always played with tilesets, and never ASCII, or “curses”. So try changing or turning off your tileset or even download the curses (non-graphical) version of the game to see if it’s visibly more responsive. Personally I’ve always gone with MShock tileset but AFAIK that isn’t maintained so much these days. So that could be one factor on my side.
So, to sum it up. If you want the quietest (fastest) possible reading spot, find a remote place and dig underground. Make sure all ant hills, house cellars, uncleared labs and slime pits are far away, and couldn’t possibly be within the reality bubble. Digging however requires some Construction skill, so a remote spot in the plains is likely OK as long as you clear the reality bubble of critters.