Im no expert but i do know that Memphis audio have speakers for all OEM locations. and they are the best sounding on the market in my honest opinion but a set of two (2) 4x6's will set you back about $120.00 but they will sound spectacular!!!!
the pioneer 4x6's dont fit, i bought a set and the magnet is too big so beware! if i were you i would go pick up a "Mobile Entertainment" magazine. That will give you a good idea for whats the best.
best of luck!
~*I want more than this world has to offer.