I drilled from the mark. That way I could ensure that the hole was where it was supposed to be, on the side where the position was critical. I have two 3/8" bits -- a brad point bit that came with my doweling set, and a perfectly ordinary 3/8" twist bit. Brad-point bits are far more precise than twist bits -- they're more likely to start where you want them to, and they're more likely to stay straight. My problem is that my brad-point bit wasn't long enough to go through 3-1/2" of wood. So I started each hole with the brad-point bit, then finished it off with the twist bit. I clamped a piece of ply on the back, to reduce tear-out.
If you're using drywall screws, you'll want to countersink the holes. Drywall screws are flat-head, and need a countersink to seat solidly. If you're using Kreg pocket screws, the way I did, you won't want to counter-sink the holes. Kreg screws are pan-head, and seat just fine against a flat surface. Both drywall screws and Kreg pocket screws are self-threading, so you don't need pilot holes in the second sheet of MDF.
Beyond the weight capacity, the Grizzly is also the largest table top on our list and in more ways than one. For a workspace, the Grizzly provides 5’ of length by 2 ½’ of width. There is not another table that really comes close to that size. Another size advantage of the Grizzly bench is the table top’s thickness. While the standard thickness of the table top for a quality woodworking bench is 1” with lesser models often offering only ¾” of thickness, the Grizzly provides a 1 ½” thick table top.