I've got a 2007 King Cab Frontier - Nismo (what they call Pro-4X now) package and a 2008 Eagle - both bought new. With BFG KO2 tires and air bags this set up works great for me. Stable, nimble, and not too big a package to use as a daily driver. I take the camper off in the winter, but it is on spring to fall. I wanted the smaller truck for the tighter 4 wheel drive roads we can have in Colorado and Utah. This set up has worked very well for exploring around in these areas, and driving in some places I probably shouldn't have
. It is probably over GVWR when packed full, but the handling is fine with the tires and air bags. You could probably do some suspension upgrades, but I haven't felt the need for them. Power is fine over passes, but I tend to drive slower on these to keep the RPM's and gas guzzling down. Does very well in 4WD and 4WD low range. Has lockers on the back which have come in handy.
There's not a lot of extra space for "stuff" with the King Cab, but it keeps the length down, and if you have the mindset of being efficient with your packing and what you bring, it is not an issue. Has worked fine for me and my wife. The "jump seats" in the back are pretty worthless for an adult - it really is a 2 passenger vehicle.
I have not modified the truck/engine in any way and it works fine for us. I have been very happy with this setup, and would do it again.