Two classics that really speak Benchmade are the 710 and the AFCK. Both are a step up from the grip. M390 steel is probably the best you can do, or maybe M4 if you don't need stainless.
You might also look at the Onslaught, which is a big knife, with a long, wide, thin, pointy-leaf shaped blade that runs just a touch over 4 inches. The blade and edge shoulder are very thin, so it's a slicer. The axis lock is, of course, great. And the full, flat-ground blade uses the Spyder hole. The steel is 154cm, which Benchmade does as well as any production company. With this steel and the thinness of the edge, it's a snap to sharpen.
Knives this large don't usually get a following -- or last long in the manufacturing line-up -- so it's no surprise that it is grossly under-rated.