Re: 1:8,7" twist in a 20" barrel
It's a metric twist, the 1x8.7" is merely what it comes out to in Imperial units. I've never seen one in a 30 cal, but that (1x8.7") was the standard twist in the 6.5x55 Sauer 202 barrels that I've used in testing. I've gone through a couple dozen of these (literally) over the years, and never had a one that wasn't an absolute tack-driver.
As far as the 30 cal twist, the extra spin won't cause you a bit of trouble. Too little spin, major problems. But spinning them faster than needed merely results in a higher stability factor, and no other problems. Don't sweat it, you're good to go.