Well, as a miner who has spent many hours with a pick, I can confidently say:

As far as higher level ore goes (Cobalt, Electrum, Gold, Darksteel), The latter three have good pick-up rates when you mine the sweet spots (+4,+2, -4 respectively... I think, haven't mined them in awhile. lol) At least maybe 50% of the 8 strikes on the node will be the appropriate item.

Cobalt however, (-4 Iron Lake) is really very terrible, and it has an additional junk item not found in say Halatali. Hate me some Brimstone +1... lol