You mean I have the chance to influence what our troops might use in the field in five or ten years? A frightening thought, in a way. But I accept the challenge!
If I were to look at a range of packs in an effort to devise the perfect pack for todays military, here are the makes I would look at, and why:
Gregory: These packs offer an excellent blend of performance, price, and durability. That companys Maven pack is a little bigger than you mention (3,000 cubic inches, $219), but it reflects much of the current thinking in a medium-sized pack. gregorypacks.com
Osprey: For some really innovative design and a lot of comfort in a very lightweight pack, look no further. Its packs feature a near-custom fit through a heat-formable waist belt, and they have excellent back ventilation. The Aether 60 is a good example, though, again, is a little bigger than what you specify (3,800 cubic inches). It retails for $219. ospreypacks.com
Granite Gear: These are very tough packs that already have a faint air of military readiness. And theyre also excellent load carriers, and very adaptable. Take a look at the Precipice (2,800 cubic inches, $155). granitegear.com
Arcteryx: What this company is doing may represent the future of backpacks. It makes extensive use of thermal-forming, for instance, and in its Naos series has pioneered packs that are fully welded, not sewn. This allows the creation of a pack that is fully waterproof without the need for a pack cover or other add-on. But, the technology is expensive. Get a Naos 45 (2,700 cubic inches, $400). arcteryx.com
GoLite: These guys are about the best around at making very light packs that still meet real-world needs of durability and load-carrying ability. Buy the Lite-Speed (3,000 cubic inches, $130). golite.com
The North Face: This company makes packs with lots of places to hang and attach stuff, which could come in handy. Get a Big Shot (2,100 cubic inches, $89). thenorthface.com
Marmot: At 7,000 cubic inches (with a $400 price tag), the Astralplane is too big for your stated needs. But this pack, which can trace its evolutionary history to the mid-1980s, has long set the standard for load-carrying ability. Its a classic. marmot.com
MontBell: This is what a stripped-down, minimalist pack that functions extremely well looks like. Get the Alpine Pack 50 (3,000 cubic inches, $199). montbell.com
There are other packs and makers out there, of course. But these cover the absolute state of the art in packs these days. Youre sure to get some terrific insights into what should constitute the next generation of load-hauling gear for the military.