Pelicans are as space and weight efficient as the shit you haul with you. How much do you need?
I pack for the trail more efficiently than most most pack for a hike, excluding two Pelicans and a couple of those Bucket Boss bags. One holds most of the tools I require, and the other protects a bagged med-kit. The bags hold other tools and things that are ungainly.
The actual outdoor gear is as tough, light and compact as I've been able to accomplish. Indeed, my entire DII has undergone a very strict diet. Unless I gear up underneath, even fully packed for pointless luxury, it still light. Well, light for a DII, anyway.
If I ever fill even half the space between the rear wheel arches, I'm either strapping something annoying down or carrying fuel.
When I decide to fill up a few Pelicans for other reasons, a few extra pounds are not relevant, and I've always found that they fit very nicely in the cargo area with plenty of room to spare, even when I've got the Engel on board.
They are rectangular, they pack and organize easily, and they fit like a glove in the back. How much space do you need? I use the rack for other things. I've never once had to expand to the rack from the cargo area because of a lack of space.
Cheers,
Kennith