First, I've talked to people (mostly younger and fitter than me) who say they notice no problems with a 30 pound load in the Exos. So keep in mind that this is my opinion, based purely on subjective experience, and is not gospel about this pack.

I find that, above 25 pounds, I can't keep the hipbelt cinched tightly enough to keep it from sliding down my hips, or trying to double over. This lets the pack slide down, which means the shoulder straps and load lifters don't function properly because I can't keep the load on my hips and off my shoulders. It also feels like the pack tends to collapse onto the trampoline suspension and push against my back. In short, the suspension just sort of stops working for me.

As I said, that's my experience - it may not be the same as others' experience.