Zombie, I harvest when they're firm with just the very slightest hint of give. Bear in mind the tom will continue to ripen - and soften - after harvesting. Don't leave it too long.
Verdun, I only grew Sungold once. Too sweet for my liking. And they tend to split if you leave them on the plant to full maturity. The only cherry I ever grow is an heirloom called Camp Joy. It's also known as Chadwick's Cherry. Will grow into a massive plant if you let it, produces tons of delicious red cherries. Send me a PM with address, etc, and I'll send you some seeds.
Here's my Camp Joy in the ground at the moment:
Mmmm. Those photos are distorted. The cherries look like a plum variety. They're cherries.