If I were looking for something tough that wasn't stainless steel, I'd be buying a Spyderco Tuff in CPM 3V (My favorite steel of all time). M4 steel is a competition grade steel, meaning its not meant to be dirty, or wet. Using it in dirtier work than cutting vegetables requires you to take good care of the blade, especially near corrosive materials.. Also Powdered steel is the only kind of steel I'll ever use in a blade. M4 is a high speed steel, not CPM (Not to be confused with the company that produces it, Crucible creates both kinds of steel.)
Conclusion?
I'd rather have something meant for dirty work (CPM 3V has more chromium, and a more simple composition due to it being a powder steel.) than something meant for a clean environment (M4 has many kinds of elements inside its complex composition, and less chromium, not all the elements in M4 are beneficial.), like a competition.