The friction bar ends will easily accomodate six or seven speed. The indexed six speed will not work well with a seven speed. One click to few but going from a seven speed set to a six cog freewheel will work.

When and if using the friction bar ends, keep in mind that the more cogs, the more precise you have to be to nail the sweet spots.

I use a seven speed indexed set of my Jamaica Bianchi and, absolutely, love them. (By the way, just a few minutes ago, Mrs. Me booked our Jamaica air fair for this year ($1,400 CND return for me and Mrs. Me)...