The F9 is a great cartridge based on the F8 actually, improved and modified to work on a much wider variety of arms. That said, the F8 is a fantastic cartridge in its own right, and the better choice if installing on the above mentioned Black Widow or Grace arms due to its more suitable compliance.
The F8-C especially so, and in attempting to procure one ended up with the L'10 instead and now a happy camper. There's something to be said for using the cartridge actually designed to go on the arm you're using, and both designed and manufactured by the same company.
I can say it was a real ear opener lol.
Martin