I go against the grain when it comes to tool cabinets and don't believe that biggest is best, especially for HOME USE (you pros don't flame me). Stacked too high and you can't even see into the top drawers. Too heavy and you can't move it around. Store your plumbing, carpentry, and seldom used specialty tools somewhere else.
With that said, I like the idea of just using a bottom cart unit, a reasonable size that you can EASILY wheel to the garage bay where you are working. The top of the bench can have a piece of plywood/chipboard so you can use it for a work place....set your tools there during the project, etc.. I LOVE this concept. No walking back and forth to the tool box...it's sitting 3 feet from your engine bay or wherever with your current in-use tools sitting in front of you at counter height. Being able to easily move your cabinet next to your work area is VERY practical.
It just requires that you give up the idea that your manhood is reflected in the size of your tool.....box.