Don't know how clean the bridgeboard software are and the Janus.library if all CGA and MDA emulation are switched of with the jumpers you might have zero picture data passsed back through the zorro2 interface, if you have some janus harddisk emulation on a lot of data will load down the zorro buss to half speed impacting your zorro3 performance
Don't know if Bridgeboard software 2.1 automatically switches off cpu caches,,,
Had dual A2088xt since 1991 and got my A2386sx around 2011
I recomend you to run Amiga Forever with your Amiga hard disk install cause AF can emulate A2386sx and save you the hassle to pull out Zorro cards and do some AF performance test
If you have an A2000 i highly recomend you to put the card there ,,, after all it are called A2386 not A3386 or A4386 :-D <3