Probikekit has a 15% off sale on their usually good price on Continental GP4000s 25 mm tires, a twinpack for $93.37, or $46.69 per tire. No shipping, no sales tax. The suggested retail on these are $75.
I've become a big fan of the GP4000s since purchasing a pair (reflective sidewall), October 2010. Nice feel, supple, light and fast. And in nearly a year of riding, we haven't had a flat, and they haven't worn out.
Now, we don't generally have to ride on bad roads, and we are a sub <300 lb team that doesn't need a 28 mm tire. Otherwise, I don't see the advantage of a more rugged tire. Had we been on Gatorskins for the last year, we would have no fewer flats (zero), but would have had heavier, stiffer and greater rolling resistance tires. The GP4000's combination of performance and flat resistance is hard to beat, which likely explain why it is seen on a lot of RAAM tandem bikes.
But, this is just my opinion based on one year of riding on these. Anybody else think that their tandem tire is The Bomb?