Bigstick,
The guys gave you good ideas on where to get a 5" system. The other part of your question"Is it really worth it or should I just stick with 4?", well that's up to you. The only performance enhancement value gained from a 5" over a 4" would be different (deeper?) sound and the visual "Oh My Gosh" factor. I didn't notice a lot of bombing on your truck, so there may not even be any "performance" advantages to a 4" over stock except for the above mentioned audio/visual. Just my $. 02.
Gene