Everyone's ears are different; what sounds good to one, may not do it for another. Make a mix of genres you'd listen to, take it to a car audio store, and play it through their setups. This won't give a 100% representation of how it'd sound (car acoustics are different), but it will give you a good idea; the only better way is to sit in a car with XX stereo setup, but that's not always feasible for the broad range of options.
In general, the rear speakers should be the last thing on your upgrade list. They are mainly fill, and you'd be better off spending that money elsewhere (better front components, better H/U, etc.).
While Kicker isn't a poor brand, there are better options for your money.
If you're looking for a decent stereo setup while on a budget, do the following:
6.5" components (front)
OE rear speakers
4-channel amp (1/2 for the components, 3/4 bridged for the sub)
Selective sound deadening