That has to result in some stiff performance penalties. Even a 486 has a hard time with faster PIO modes, if you have an Am5x86-133 overclocked to 160 MHz and toggle the turbo button, you can watch a large disk transfer speed up and slow down in real time.
A fast 286 is going to have terrible performance, especially managing multiple drives. Though I guess there's a price/performance tradeoff. If they had included a full 486 on the card, the card would have been way more expensive. Though it is strange that they'd use a 16 bit processor on a 32 bit bus.
I wonder if you could do something silly like attach one of those 286 to 486 upgrades to the card and see if it works, and if it works any faster than the stock CPU lol.