No, I have not tried a W taper. It is going to be really sensitive in the middle of the adjustment and easier to tune (not as sensitive to adjustment) at the extremes of the pot travel. I'm interested to see how this works out for you, what you think of the finished product.
I have only built a single unit of the slider version, but I have parts to build two more when I get the enclosures made. On one I will adjust some components on so it will (hopefully) work well for a bass. I really like the one I have, it makes a big difference in my sound.