are very large beets any good for eating?

I just got a batch of beets in my CSA bag. Some of them were white beets, and one of them was huge! I roasted it with some thyme, olive oil, and salt for about 1 3/4 hours. It came out perfectly cooked and it surprisingly sweet! So have no fear about bigger beets for roasting.

Lemon is a great choice :D

In my experience, larger beets aren't as sweet as smaller, younger beets. However, you can maximize their flavor and sweetness by roasting them. I rub them with olive oil, wrap them in aluminum foil and roast them in a baking pan in the oven at 450 for about an hour. Let them cool slightly, then rub the out peel off, slice them and enjoy!

You can always make a dip of roasted beet with tahini and lemon.

All else being equal, a very large beet will be more dense and somewhat less tender and sweet than a small one of the same variety. But if well grown, it will still be perfectly good to eat. Beets are less prone to getting woody when large than other root vegetables like carrots or turnips. I like to let a few beets in my garden grow to softball size before harvesting; they keep a long time and still taste fine. In France, markets routinely sell very large cooked beets for grating or dicing in salads.