A heavy duty screw that Simpson Strong-Tie makes that I've been impressed with is their SDWS timber screw line (e.g. https://www.lowes.com/pd/Simpson-Strong-Tie-Strong-Drive-174-SDWS-TIMBER-Screw-Exterior-Grade-8212-0-220-in-x-3-in-T40-50-Qty/1002703078) - they are marketed as an alternative to bolts and they allow for some pretty intense pulling power (it's hard to tell from the picture how big the head and shank are). I originally found the SDWS line when looking for screws that were officially rated as a framing screw since deck screws are not.

If you find that you need more rigidity, you could add diagonal bracing along the back and sides, though this will likely detract from the aesthetic and may be overkill for a work bench.