Well, you couldn't plug a cable from a peripheral directly into a PCI port in 1993. It wasn't an external interface at all.
PCI was an internal "close to the CPU" communications method mostly routed through a motherboard, superseding ISA which was the CPU bus physically extended into slots. ISA ran at 8Mhz (maybe 10Mhz or 16Mhz, memory is funny) which was also pretty fast in 1993.
It wasn't until PCIe introduced switching and Thunderbolt that PCI-anything became more like switched Ethernet and something that could be funneled through cables.
> ISA ran at 8Mhz (maybe 10Mhz or 16Mhz, memory is funny)
The answer is "It depends", but it also depends on what you mean by ISA? The slots in the PC, XT, and AT (and clones of the appropriate vintage) tended to run synchronously with the CPU, which meant the performance of a card would depend on how fast your CPU was - well, up until the point where it was excessively overclocked and stopped working, of course. This meant that old cards wouldn't necessarily work in newer machines, given they may have been designed to work with a 4.77MHz PC. Later systems supported dividing the CPU clock to get back down to around the 8MHz range, and eventually we get to the point where the ISA slots aren't connected to the CPU at all but are bridged to PCI. But the term ISA wasn't really a thing until vendors introduced EISA as a royalty-free competitor to IBM's MCA slot architecture, and retconned the AT slot into ISA, and at that point things had pretty much settled on 8MHz. So, in that sense, ISA has always been 8MHz, even if the thing that was identical to ISA wasn't.
There were actually PCI and PCI-X external chassis boxes (in all 4 forms), they were expensive as hell, but they were a critical tool for developing PCI/PCI-X devices.
They usually used 1 or 2 scsi-3 (80-pin) connector to connect from the host to the box (I think you could get away with 1 connector on either 32bit standard if you dropped some of the non-vital signals).
To expand on the above, absolute theoretical 16bit ISA limit is 2 cycles per transaction (0WS), (2 Bytes x clock MHz)/2 cycles = ~8MB/s at 8MHz. In practice best period correct VGA cards reach ~4-6MB/s write speed. Slowest VLB cards do ~10MB/s fastest ~30MB/s, slowest PCI VGA ~15MB/s fastest again ~30MB/s.
PCI was an internal "close to the CPU" communications method mostly routed through a motherboard, superseding ISA which was the CPU bus physically extended into slots. ISA ran at 8Mhz (maybe 10Mhz or 16Mhz, memory is funny) which was also pretty fast in 1993.
It wasn't until PCIe introduced switching and Thunderbolt that PCI-anything became more like switched Ethernet and something that could be funneled through cables.