if I remember correctly the 386 didn't have branch prediction so as a thought experiment how would a 386 with design sizes from today (~9nm) fare with the other chips?
It's not just the lack of branch prediction, but the primitive pipeline, no register renaming, and of course it's integer only.
A Pentium Pro with modern design size would at least be on the same playing field as today's cores. Slower by far, but recognisably doing the same job - you could see traces of the P6 design in modern Intel CPUs until quite recently, in the same way as the Super Hornet has traces of predecessors going back to the 1950s F-5. The CPUs in most battery chargers and earbuds would run rings around a 386.
Bear in mind that with an 386 you can barely decode an MP2 file, while with a 486 DX you can play most MP3 files at least in mono audio and maybe run Quake at the lowest settings if you own a 100 MHZ one. A 166MHZ Pentium can at least multitask a little while playing your favourite songs.
Also, under Linux, a 386 would manage itself relativelly well with just terminal and SVGAlib tools (now framebuffer) and 8MB of RAM. With a 486 and 16MB of RAM, you can run X at sane speeds, even FVWM in wireframe mode to avoid window repaintings upon moving/resizing them.
Next, TLS/SSL. WIth a 486 DX you can use dropbear/bearssl and even Dillo happily with just a light lag upong handhaking, good enough for TLS 1.2. Under a 486, a 30-35? year old CPU. IRC over TLS, SSH with RSA256 and the like methods, web browsing/Gemini under Dillo with TLS. Doable, I did it under VM, it worked, even email and NNTP over TLS with a LibreSSL fork against BearSSL.
With a 386 in order to keep your sanity you can have plain HTTP, IRC and Gopher and plain email/Usenet. No MP3 audio, where with a 486 you could at least read news over Gopher (even today) will multitasking if you forced yourself to a terminal environment (not as hard as it sounds).
If you emulate some old i440FX based PC under Qemu, switching between the 386 and 486 with -cpu flag gives the user clear results. Just set one with the Cirrus VGA and 16MB and you'll understand upong firing X.
This is a great old distro to test how well 386's and 486's behaved:
ISTR the cheap "Pentium clones" at the time - Cyrix, early AMDs before the K5/K6 and Athlon - were basically souped-up 486 designs.
(As an aside - it's very noticeable how much innovation happened between a single generation of CPU architectures at that time, compared to today. Even if some of them were buggy or had performance regressions. 5x86 to K5 was a complete redesign, and the same again between K6 and K7).
Nowadays I think it's still doable in theory but Linux kernel have some kind of hard coded limit of 4MB (something to do with memory paging size).
ELF supports loading a shared library to some arbitrary memory address and fixing up references to symbols in that library accordingly, including dynamically after load time with dlopen(3).
a.out did not support this. The executable format doesn't have relocation entries, which means every address in the binary was fixed at link time. Shared libraries were supported by maintaining a table of statically-assigned, non-overlapping address spaces, and at link time resolving external references to those fixed addresses.
Loading is faster and simpler when all you do is copy sections into memory then jump to the start address.
And yet the disk sizes where't that big (and tons of people still had less than 10GB).
386, both SX and DX, run 16bit code at ~same clock for clock speed as 286. 286 topped out at 25MHz, Intel 386 at 33MHz. Now add the fact early Intel chips had broken 32bit and its not so beastly after all :)
In one of Computer History Museum videos someone from Intel mentioned they managed to cost reduce 386SX version so hard it cost Intel $5 out the door, the rest of initial 1988 $219 price was pure money printer. Only in 1992 Intel finally calmed down with i386SX-25 going from Q1 1990 $184 to Q4 1992 $59 due to losing AMD Am386 lawsuit, and only to screw with AMD relegating its Am386DX-40 Q2 1991 $231 flagship to the title of Q1 1993 $51 bottom feeder.
A large reason why out of order speculative execution is needed for performance is to deal with the memory latencies that appear in such a system.
By the time of 80486, motherboard cache sizes had increased to the range of 128 to 256 kB, while 80486 also had an internal cache of 8 kB (much later increased to 16 kB in 80486DX4, at a time when Pentium already existed).
So except for the lower-end MBs, a memory hierarchy already existed in the 80386-based computers, because the DRAM was already not fast enough.