Jonmok,
The 705 and the 710 have the same basic shape, but the 710 has a longer blade. The blade shape is drop point that has a slight recurve in the larger blade. The 710 is available in 154CM and M2 steels, while the 705 is only available in 154CM. M2 takes a sharper edge and holds it longer, but is difficult to sharpen on a Sharpmaker. 154CM is as sharp most folks will ever need or want, but you'll yearn for M2 if you have exposure to it. The handles are made out of g10, a really tough epoxy/glass mixture that just feels good in the hand.
The 720, 721, and 722 have bowie or tanto blades (one has a tanto and the other two have bowies). One of the bowies has aluminum handles and the other has G10. They're available in 154CM steel.
The 730 and the 735 Ares have a 154CM steel spearpoint blade and very nicely shaped g10 handles. There are about 500 models floating around with carbon fiber scales and M2 steel. There was a 732 which had the same shape with a different colored handle. It also had M2 as an option for its blade steel.
The 750 is a discontinued model with a framelock instead of an axis lock and a recurved 154CM blade.
770 through 773 are gentlemen's folders with handles ranging from aluminum to carbon fiber with 154CM steel spearpoint blades. They're very classy, but not comfortable to some users.
That's the 700 series to the best of my knowledge and I own and have had good experience with the 710, the 730, and the 730CFHS. I think Benchmade's best production model is the 806D2 even though I'd prefer it to be smaller. My favorite is the 921 Switchback.