Steel nut or aluminum nut?

For some reason I assumed an 8.8 stainless steel nut, that's where I got the 6 and 10Nm for M5 and M6, respectively, but I don't know. It is Shimano SLX 2*11 shifters. I don't know the material of the clamps. Perhaps I can find a manual on the net.

Is the bolt a tight fit into the nut (without the brake body to get in
the way), or is it flopping around loosely?

No, everything looks and works great!

Did you grease, lube, anti-seize, or Teflon tape the threads? That
will decrease the maximum torque.

Yes I know, see the OP. So no, no grease.

The thing I wonder at the moment, assuming I got lucky and there is no damage, should I still loosen it up? What will happen if I run into a tree? Will the high torque or the low(er) torque be better then for the bike?

BTW on the handlebars are a couple (6?) of M5s. There they say explicitly max 6Nm. Which is the max for M5s. I tried all of them with my torque wrench set at 6 and they were all at 6 or higher already!