Honestly, the picks don't seem to make quite as big a difference as the axes do. I'm sure they do, but it isn't as obvious. I have a legendary pick finally, Fierce I believe so it has discovery and something else, and it doesn't seem a whole lot faster than the exceptional Raes gave me long ago even though the stats are significantly better. I made an exceptional rubicite axe, however, and beefed it up as much as I could (5 slots), and it is noticeably better than the green (superior?) I had. You can count how many chops it takes, for one thing, even if you can't really tell how much faster the swings are. My green axe takes 11 chops for the smallest tree, whereas my blue takes 6. That's a HUGE difference, not even considering that I swing faster too. Once I harvest the diamonds required to make it legendary it will be even better.
Speaking of those diamonds though...fuck that is annoying. I have thousands of rubies at all times, but diamonds are so hard to find, yield so few when you actually find them, and tons of them are used in the upgrades. I get that there has to be some limiting factor so I don't just make dozens of legendaries, but still, diamonds are the fucking worst.