I used the 6'10" for a couple months and liked it but at the time they were too pricey, no you can get them cheap or just go with the 7'2 MXF Cumara.
The 6'7 was ok, just too short for my liking. I used it for my dock skipping rod for tubes on a jighead and the Spot Remover.
(I have a buddy who is sponsored by Fenwick so I mess around with a lot of their stuff but have never actually bought one) I don't think you will find a large difference in sensitivity from a $100 drop-shot rod or $250 rod. All depends on the actual weight of the rod and type of weight imo.