Oddly, just yesterday I published an article about multicore CPU performance of some providers (including DigitalOcean) and they now have made my tests almost obsolete. Luckily, my tests were with $20 VPSes so the still have some credibility.

But I'm curious how oversold would the new droplets be. DO had the most deviation in the providers that I checked. Would think that at least for a while, there should not be much overselling on CPU.

Interesting, but is there a way to upgrade existing droplets?

Does not seem so (checked with a new droplet), which makes sense. The high CPU droplets have only 20GB of storage which would make any standard droplet, except the $5, inconvenient to resize automatically (if not impossible or very dangerous).