I'm assuming you're concerned about the pins themselves and not the wood. I spoke to a tech at KV and their shelf pins, 5 mm or 1/4" are rated for 60 lbs in Red Oak. I'm planning on 2 or 3 per shelf end which would have a 240 lb or 360 lb failure weight. Also, I'm going to use 7 mm pins.
60 pounds really isny much, doubly so when manufactures always lie on capacity ratings, triply so when the shelves themselves would weigh ~25 pounds. Not to mention, sag calculator or no, 6 feet of wood supported only at the ends is going to sag over time. Those sag calculators only show sag that would happen if you set it up, put some weight on and measured immediately, not a month down the line.
Going with a torsion box assembly for the shelves, as Al suggested, is a good idea, if rather labor intensive. Id also second the vote on rethinking the shelf pins. Even if we assume that they actually are rated at #60 weight, and even if we assume that the load would scale linearly across the 6 pins, youre still supporting a lot of weight on not a lot of surface area.
Although, i suppose a good question to ask would be why you need the shelves to be adjustable? Makes sense on mass produced pre-fab furniture, because theres no way for the manufacturer knows what height every consumer wants the shelves to be, but on custom made furniture the same doesnt hold true. So why not just dado it?