Just not sure If I need the HDs If I am loaded down to 600lb or so only on trips and not the 75% of normal Hwy driving with out the load.
Ah! The ultimate quest of a pickup truck owner!
HD leaf springs present a compromise when it comes to part time duty. I suspect you won't like the ride and handling you get for that 75% unloaded driving you do. However, you will appreciate how well the HD Dakars support and manage your
loaded down Frontier. If you get a medium duty spring, you might not be pleased with either loaded/unloaded scenario.
Luckily we have a heavy aftermarket bumper and a camper shell on our 05 Frontier all the time, which makes driving around with the HD Dakar springs a reasonable prospect. I'm pretty satisfied with it, but I'm more satisfied with how they work when loaded. That was my priority when I bought them.
Your priority sounds different.
You'll be hard pressed to find a replacement leaf spring pack or AAL (frankly, forget the AAL) that can both be comfy on the road while totally unloaded Monday through Friday, and then come weekend support a heavy load while off highway. It's just two different demands.
The HD Dakar springs are pretty cool, but I caution you if your highest priority is keeping a comfy ride with a virtually unburdened back end.