I like the 25 in front 23 in back thing, too, though i'm not doing it anymore. On my last bike I liked to get something really tough and grippy in the front, and then a tough slick in back. The vittoria randoneur (some people complain about the ride on these, but I thought they were fine) + rubino (I agree, these are good tires for the price) was a good combo. That way I got the best of both.

Now I run 23s both front and back (vredstein fortezza) but I'm also skinny + light so that makes a difference in tire size choice.