MT than Diablo isn't so bad. I've done it that way several times, riding over Marsh Creek from Antioch. This time of year, I worry about the heat. There's not much shade climbing Diablo and quite a lot on MT.
I've done the climb up the Plunge, there's almost no shade, and descended down the Clayton side. The descent is really not that bad, if you just understand that you're not going to have a flying descent, control your speed and watch for the potholes.
For future summer rides maybe you could start at the Lafayette Bart station or Walnut Creek, that puts you a little closer to Danville, so you could do Diablo first, if that's your pleasure.
Have a great ride tomorrow!
Veronica