I have been using AutoCAD 2010 since around 2012, and while it's not anywhere near as fast as AutoCAD 2002 that I use for most design, I was forced into this new (at the time) program because dealing with vendor's drawings basically required it.
Since I've had 2010, I've been down-converting vendor files to 2010 for speed, but lately I'm getting a LOT of AutoCAD 2018 files, so I figured it's about time to move to the new software.
Testing at work, it seems AutoCAD 2018 is about 1/2 as fast as AutoCAD 2010 overall. I conveniently have some VB macros that time how fast things happen, and most of the issue is the load time for files; actually processing the file is about the same speed (though it is ALSO slower). I've tried comparing ObjectDBX vs "Editor", to try and eliminate the videocard as an issue; similar slowdowns.
I've tested with a few systems, and with a few different processors, and found that outright single-thread clock speed is basically the only number that matters, but I can't find out why AutoCAD 2018 is so much slower than 2010. I thought it might be the licensing server, and even installed it to a RAM drive, but it had no impact.
I have already disabled all of the Infocenter stuff, AutoCAD 360, and installed the offline help files, but none of that impacts anything significantly. It seems to be basically how fast AutoCAD can load a file that is the issue, and there seems to be no reason for it to be so slow. I've uninstalled and reinstalled AutoCAD, with no change. All AutoCAD versions are up to date. All drivers on the PC are up to date, however I've tried swapping videocards/drivers ("Pro" vs "Consumer"), and storage controller drivers with no noticeable impact. Even tried moving to a Ryzen system, just in case, but same-ish results.
On my primary system, AutoCAD 2010 takes about 2 seconds to load, AutoCAD 2016 takes about 4. If I load a random selection of files (so, after AutoCAD is loaded, select these 10 files to load), it takes about 8s for 2010, and 19s for 2018. While that doesn't seem like much, a lot of my work is opening a file, doing something random programmatically to it, and save/closing it; something taking 3hrs vs 7hrs to run matters.
Is AutoCAD just getting THAT bloated over the years? It doesn't seem like anything that matters is being added to the software, so it surprises me that the file-loading subsystem would be so much slower.