Accuracy was one of the major reasons for 86Box forking from PCem. PCem's development was spearheaded by a developer that cared more about playing specific games and took shortcuts to get there.
86Box is far more focused on being as accurate to real hardware as possible, allowing all kinds of old software to run, even the hard ones like OS/2 with its heavy uses of ring 1 and 2 security contexts that are usually entirely ignored by OSes like Windows and Linux (or, well, DOS, where literally everything is ring 0...). It can even run the 8088MPH demo made for the original PC :-)
With this shift in development focus, it pretty much necessarily sacrifices performance for the goal. They are often incompatible goals. See how emulators like Nesticle could run just a handful of NES games on a 486 compared to later developments like Nestopia that demanded a Pentium 4 to run full speed, but do run every NES game ever made.
86Box is far more focused on being as accurate to real hardware as possible, allowing all kinds of old software to run, even the hard ones like OS/2 with its heavy uses of ring 1 and 2 security contexts that are usually entirely ignored by OSes like Windows and Linux (or, well, DOS, where literally everything is ring 0...). It can even run the 8088MPH demo made for the original PC :-)
With this shift in development focus, it pretty much necessarily sacrifices performance for the goal. They are often incompatible goals. See how emulators like Nesticle could run just a handful of NES games on a 486 compared to later developments like Nestopia that demanded a Pentium 4 to run full speed, but do run every NES game ever made.