I don't what know what you would gain.. I think if you went to 1k each you might want to think about building a new box and tuning it around 30hz with more port area. I am happy with the 4 but at times I feel like it should be louder. At the moment I have a IA Death Penalty/PSI 21" sub in a 10ft^3 box sitting on top of my seats in my crew cab and it is so much louder than the 8's I can't describe. I think I need to build a bigger box tuned lower for my 8's to get the output I think I should be getting.