I find myself in possession of two sets of new 700X23 tires: a pair of Continental Grand Prix 4 Seasons, and a pair of Specialized All Condition Armadillos.
I have alternated between the two sets of tires and noticed some interesting differences.
The Continentals have better grip, they handle road irregularities more gracefully, they accelerate surprisingly well, and they have significantly lower rolling resistance on the level.
On the negative side, I may weigh too much for the Continentals (225 with full messenger bag) and the rear Continental feels a little vague, as if it doesn't have enough pressure (I run it at the recommended max of 120psi).
In favor of the Armadillos, the rear Armadillo feels crisp and in control at 120psi, the Armadillos climb much better (more efficiently) than the Continentals, and, of course, I trust the Armadillos more with road hazards (even though the Conti's have significant flat protection).
I note that my last four flats all occured on the rear tire.
I also note that when I fell and punctured my lung last March, the front tire went out from underneath me.
What if I put a Continental on the front and an Armadillo on the rear?
It seems to me I would gain in climb efficiency and rear tire road hazard protection; and I would also gain in front tire stickiness, handling, and comfort, with a lighter tire, less rolling resistance, and enough flat protection for a front tire.
I wonder though if someone knows a reason why I should NOT do this.
By the way, if I had to choose between one tire or the other, I couldn't do it.
They each have such definite virtues.
I guess I'd flip a coin.
Presently, I change them to match the weather, putting the Conti's on when it rains.
IRO Mark V pro (RIP), Bianchi Giro, Giant Xtc1, Redline Conquest Pro, Kelly Deluxe singlespeed.
I use some conti grand prix 3000s which I believe are very similar to the 4 seasons. Not that it really answers your question, but I find that I solve a lot of the problems you talk about by running them at 100psi instead of the max rec. pressure. I am not sure what you mean by "vague" however my interpretation of it indicates too high of a pressure as opposed to too low.
I just replaced my rear tire today and still have mis-matched tires. I see no reason to resist mixing. I've got a Hutchison Carbon Comp in front and a Specialized All Conditions in back. Before I had the Hutchison and a Conti Ultra 3000, and before that a Conti Ultra 2000 in back.
Outside of looks, I really can't come up with any good reason to not run whatever tires you want without matching them up.
I put an Armadillo on back and a Continental Grand Prix on the front and what a difference.
My son and I just got back from a 24 mile ride and the bike climbs better, handles better, rolls faster and feels more comfortable on rough and cracked roads.
I feel as confident about flat resistance with this combination as I did with Armadillos in front and back.
Big improvement all around.
I think I will stick with this combination.