What types of music do you prefer?
From what I understand after speaking with Louis is that the AlNiCo drivers excel at Jazz, Acoustic and Vocal stuff and the Ferrite drivers excel at Rock and more fast/dynamic range stuff. It's not that AlNiCos would sound bad playing Rock or vice versa that the Ferrites don't play Jazz good, it's just that their forte is like as mentioned. I play a little of everything, however probably 80% of my music is Rock based so Louis suggested the Ferrite drivers and out of the RS5 vs. RS7, I chose the RS7 drivers.
I think what you give up in regards to the different Ferrite based drivers such as RS5 vs. RS7 is that the RS5 are faster and the RS7 go a bit lower, but not quite as fast. Both the Ferrite drivers are more efficient than the AlNiCo's, so they are easier to drive in that regard so you may get a little more volume out of them.
I use my RS7 speakers with a Decware Taboo MK II @ 6 watts and they are a great all around speaker. I use them for both movies and music and I also use a sub (especially with movies).