Spec
3/4" Melamine 36" wide WILL sag some. Put a lite rail at the bottom to help stiffen as well as give better looks. Hide it behind the doors if very contemporary. Try to avoid cabinets over 30" wide for optimal results with the shelves. Consult the AWI Quality standards if in doubt.
Metal drawer systems: Depends on how you are set up and price point for your clients. Best bang for the buck, and rugged, use Zargen by grass. Easy to Mfg if you have the proper grass machines, a pain if not. Nova Pro is a sweet system even without any of their dedicated machinery. Good price point for what you get as well. Less SKU 's to deal with than Tandembox.
Legrabox: a bit more effort to mfg (than the Nova-Pro), and more many more SKU's to deal with but the finished product is excellent! FWIW I think the Blum Products have the edge on the final fit & finish, but Grass's products seem to be geared towards better/simpler manufacturing. Also, Grass has a new 1/2" thick sided drawer.... Vionaro? Nice thing about this one is they use the same runner as their undermount guide, less SKU's to keep on hand! I look to try that our when I can get it. The older systems: Nova-Pro & tandembox will be dropped in the not to distant future I suspect, replaced by these newer systems.
Be precise with Metal systems!!!! -enjoy