How much difference you get in performance depends on several variables, including: How well the strings are made (better made will generally be a bit faster than poorly made), the mass weight of each (this can be affected by how much serving you use, what size serving, wax content, even the string material color--white or natural is the lightest), nock fit, your release, bow design, draw weight, draw length, arrow weight, tuning, how well the arrow is matched to the bow, etc. etc. etc. 8-10 fps is on the high end for most, but not out of reason.
For me, the performance difference isn't even in the equation. I prefer the increased stability, consistency, and durability of a well made "ff" string. (some of which you will loose if you go with an extreme low strand count).
A properly made endless loop string will have some twist in it, and you can add or remove a few for length adjustment if needed--just not usually as much as you can with Flemish.
Of all the available materials, my personal favorite is BCY-X. Dynaflight '97, 8125G, Mercury, and 8190 (F or Universal) are also very good.
Side note: Materials made from SK90 Dyneema (BCY's materials include 8190 and BCY-X) won't be available much longer, at least not in the current blend. SK99 Dyneema is taking the place of SK90. 8190 string material will be discontinued, BCY-X will be re-formulated to incorporate SK99. Mercury is already made from SK99. When current supplies are exhausted, that will be it. The new BCY-X will likely be available around the first of the year, if not sooner.