Like Mort, my sparge water runs about 190. I've never seen the grain bed go over 170, so no tannin problems. Because I control my mash pH, I'm not certain I'd have to worry about tannins even if I used hotter water. In short, sparge temp should have nothing to do with attenuation UNLESS you have a significant amount of conversion left to happen after your mash time. That's very unlikely, and if it's what's happening, you have a different problem to deal with. But I expect that should show up as low efficiency.