Sliding friction is always greater than static friction, except in the case of a few things that exhibit this "law" in the wrong way, like that viscous fluid stuff, the tires still have friction with the road surface, just not much. Although the same people who say this can't explain why wider tires have more friction than wide ones, but tests have shown it true.
If anyone can find a traction graph of Cf vs %of slip it would be cool, especialy a newer tire, maybe two one of a race and the other street.
I have always been in the "when in doubt gas-it" group and it has gotten me out of trouble on two and four wheels, once though I overdid it and it resulted in a big burn out at speed in my car which spun around a bit while I had it floored, thinking "just a little more gas" so that I can get the weight transfer for more traction, thing is though is vaporizing rubber is a better lubricant and smokescreen than anything else.
One thing I have noticed is that slippage is best for traction on dirt and ice, and they are using a lot more slip, and wear is detrement to the performance of studs and dirt tires. So why is that? I imagine there are no hard numbers as the speedway and flattrack guys are so anti-technology and more old school.