I would not go with either the 5x7 or the 6x8 i would go with 6 1/2 all the way around. I would do the front with Infinity Reference 6000cs, I would realy go with the kappa but its to high of a price then what you were looking for.
these are $199 crutchfield and you can find them some where else cheeper.Infinity Reference 6002i these for the back there $99 about 300 for the hole thing. They sound ok off the HU if you put the 50rms into them they sound much better.