I've personally never had an issue with sliding forward using this seat. I will say I have a bigger frame clocking in at 5'10" 240ish lbs. I have found it very comfortable and it had enabled me to do long distance touring.
The FZ6 was an awesome bike for 9 years. It was so perfect I had trouble justifying getting a new bike.
The seat was plenty comfy.. it accompanied me to far off places like N. Carolina, Upstate NY and Maine. I wish I could just transfer it to the new bike but hence it has to be for sale.
Congrats on the new bike. I too am looking at making the decision to move on from the FZ6- and not because its a bad bike but I think I have one more new bike before I hang up the helmet. Truth be known I have great misgivings about parting ways!