5mb/s is on the low side. Isa ran on the same clock as the cpu. We started there, but things got better quickly.

I think the hard limit was a bit below 40MHz, as people still used 74HC chips for glue logic. Combined with EISA 16 bits = 2 bytes per cycle this might give you a 80MB/s theoretical EISA peak. I had an EISA based 386 running 40MHz at the time.

Interestingly, VESA's 133MHz is double this, so maybe the majority of the speed gain was doubling bus width to 32bit?