Hallelujah! Here’s what technical support recommends: “disable the double click assist within WACOM control panel.” Of course, nothing in the control panel really matches the description, but here’s what works:

And it works! The tablet no longer lags, and works better than my old PC tablet (it was a serial port model, so it just couldn’t keep up).

Of course, it’s a bit pathetic they’d release a driver that offers to assist double-click, and activates the functionality by default, but can’t do so without making the whole computer lag; besides, unlike the Windows version, the OS X drivers don’t allow you to define application-specific, so I can’t ask it to deactivate double-click everywhere but in the Finder. But what matters is, it’s working now, and I can draw (yes, I do plan on improving someday) and write. Hurray!