I think the problem is with the 8288...must be a 82C88-10 and is not able to give the good timing at 16mhz...
Same problem with the 8284 ; the 82C84 need a different circuit for the Xtal (no 300 ohms resistor and 20pf capacitor to ground instead),and the external clock is limited to 25mhz,good enough for 8mhz turbo,extrem limit 30Mhz for turbo 10Mhz.
the µPD71084C and µPD71088C-10 are not better.
Another problem is that my XT clones run in turbo mode after reset , before checking the turbo switch and selecting the clock source of the 8284..
If they don't crash,the card is running correctly in 4,77 only after switching the clock,but most of the time they crash before and you need try minimum 10 time reset even you select no turbo.
sorry for my poor english