Well, as far as my shelves go there are made out of oak playwood with the solid oak edging like you said. As far as sag goes I'm not really to concerned about it because the heaviest peice of gear that will go on the shelves is the 990. The 7700 will be on the bottom shelf this time instead of next to it like it was with the last cabinet I built. As far as the bottom shelf goes there will be 6 casters on the bottom (1 in ea. corner and 2 down the center) which will prevent it from sagging.