The ULA Circuit might be the Ghost replacement you are looking for. Both packs feature Delrin suspension hoops and both are great for middle-range gear weight. As for volume, I believe the pack bags are comparable in size; the Circuit's greater overall volume results from its voluminous mesh pockets.

While I don't have any direct experience with the ULA pack, I do have a hiker friend who owns both Circuit and Ghost and love them both.

But if panel loading is the feature you are looking for, then the Golite Litespeed is worth a look.