What for rear speakers?

This is almost like asking "what's better...pepsi or orange soda?" It's a subjective choice.

Now IMO rear fill is not very important to me, but a consideration. I like my stage to be just that...a stage so I like to have as least possible pulling that stage to the rear. However ,regardless of what speakers you choose, it can be faded or adjusted to taste.

If money is no object you might as well use the same model you use for the front, I believe those trucks use the same size factory speakers front and rear. If rear fill is not as important, and saving some money is go with a lessor expensive replacment speaker and make sure you don't overpower and destroy it.

Hope I helped.