You hit the nail on the head in regards to the differences in DFK between Tiff, and Tara. Tara is light years ahead in the DFK game, and is the primary reason why I much prefer to see her over Tiff. For some reason, DFK is a must for me - otherwise, it just doesn't feel like much of a turn on.
Also, same as Virgil, I've seen both of these girls and there's not much I can add to the reviews. These girls are amazing - my next up will be having a double session with them. I've already seen Tara twice, and Tiff once.