386 is actually somewhat slower clock for clock than 286 for same 16bit code. So no, no optimizations. For example https://web.itu.edu.tr/kesgin/mul06/intel/instr/movs.html, 486 was only slightly optimized, it was Pentium where they finally started working on IPC.
Right, the 486 was only slightly optimized for IPC. Most of the 486's performance over the 386DX was from its L1 cache (or just called CPU cache at the time, there weren't different cache levels yet.) You can turn the cache off in a 486's BIOS and it will be barely any faster than a 386 of the same clock speed.
