Dibble Donkins

I have a Trek Fuel EX9, and sometimes take it on downhill rides that it can handle. A lot of the time it's doing "all mountain" or whatever you wanna call it (trails that have more climbing/flatland than straight downhill, usually with a good amount of rocks to grip over).

So usually, given I mostly do non-downhill, I would think a bigger tire should go on the rear (to help grip when climbing and all that). I'm trying to balance this bike a little more towards downhill though, and was wondering what the rule of thumb is for downhilling. I would think that for downhilling you want a larger front tire.

I just got a Maxxis Minion 3C EVO 26x2.5 tire ($80, jeez) and threw it on the rear. I'm wondering what should go on the front now. Another 2.5?

It seems like I'm trying to have my cake and eat it too, so maybe to get the most grip out of both worlds, the front should be 2.5 also. What do you think? I don't really care if it slows me down either way on flat or downhill, my concern is traction, for both flat and downhill riding. Also, I generally don't ride when it's wet out, so I don't care that the 3C EVOs are harder rubber (and I like that they may last longer than softer compounds I've tried in the past).