I have hit and played both the 670 and 712 mb blades so I can help with one opinion anyway. The 670, in my opinion, is the very best muscle back Titleist has ever produced. Small compact head design, deep heal and a thicker top line all contribute to their awesome performance. This club is strictly a players club and should be used by a low handicapper! The 712 is solid and has a longer toe to heal length with a thinner top line. Feel is very nice! Performance is exceptional. Both the 670 and the 712 must be hit in the center of the sweet spot to get all of the intended shot. There is no backup forgiveness like the AP2 or the CB. For me, and I still play with a beautiful set, the 670 is the best there is. Get ready to take your game to a different level! Practice hard and these mb's will be all you could hope for!

The 670 was a compact blade with a squarer look to them.  They had a slightly wider sole with a little more camber and bounce for aggressive players that had a steeper swing.  The 712 MB's took parts of the 670, 680 and 690's and created an MB that had good turf interaction, smaller topline and slightly less bounce .  It has minimally more offset on the longer irons and minimally less on the short irons.  Good choices to have :)

Definitely, Cathi. That's why I chose to get a set of 712 MB's. The new MB's combine the best of the best. I had a set of 670's and loved them. They're great clubs. However, the new 712 MB's are more workable, look GREAT, etc., and the performance/consistency and feedback are wonderful. 

In no way shape or form should you swing the 670's.....have someone else in the family carefully box them up.......and send them to me, I will happily take care of them for you.