We run continental gatorskin 25's exclusively on the tandem. If you scan this forum and the T @ H list, you'll see a lot of discussion about continentals being prone to sidewall failure, so I watch them pretty closely. In fact, I've changed out every one due to beginning to see degradation of the sidewalls, but we're getting about 1,500 miles from a rear tire and around 2000 from the front.
Those tires can be buggers to get on the rim. In fact, they're almost impossible to get on the rims on my single, so I've stopped using them there. It's still work on on the tandem wheels, but at least I can get them on without having to resort to a tire tool.
Our team weight is 285.