I've just done some research on this myself. The 617 is a seven shot .357 in the Taurus Compact frame, same as the 450, 460, and their tracker series. The compact is slightly bigger than the small frame that the Mod. 85, 605, or the new CIA series uses. I had ordered a 617 and called back to change it to the 651. I wanted to be able to carry this gun in my pocket and the compact frame is too large for that. I have a Mod. 450, which is the same size as the 617. If you look at the difference in the two frames you'll see the main difference to be in the height. Hope this helps.
Don