If you haven't already done it, try adjusting your silencer placement--that can make a huge difference. How your nock fits, padded loops, how the string is made in general, etc. can also make a difference.
Some bows seem to "like" certain materials over others, some don't seem to care one way or the other.
I won't use dacron on a bow that will handle Dynaflight '97, and very rarely even shoot a dacron-only bow. I own a couple, but only for sentimental/collector value. I've got a Dynaflight string on my selfbow, because with dacron the hand shock is just too much. I gets lots of comments on how quiet my longbow and selfbow are, and both keep a Dynaflight string on them.
How much more stretch you'll get with dacron depends on the strand count, draw weight, draw length, temperature, etc. If you unstring your bow, it will draw back up some and have to settle back in. Heavier bows/lower strand counts will stretch more. They will stretch more in hot weather vs. cold. I don't know if they ever completly stop stretching.
The benefits I notice the most with Dynaflight (and other low-stretch materials) are much less hand shock, much less stretch/creep, and a much stronger/more durable string. I'd use it if it were slower than dacron.
The speed difference also depends on the variables of strand count, how the string is made, etc. Most probably average 5-10 fps, but it can be more.
I've personally never seen a bow that was made to accept FF type materials damaged by a properly made string. I've only seen two damaged by a string at all, and these were old bows with improperly made strings. I have seen several bows that broke/failed with dacron strings. I'm not blaming the dacron string, but generally speaking if a bow fails and has a FF type string on it, the string gets the blame. If it has a dacron string, something else gets blamed. I've been using Dynaflight on my main bow since just after the material hit the market, pulling 66# at 30.5". I hunt with it, play with it, and shoot lots of 3-D tournaments with it. I have no idea how many thousands of arrows have been shot throught it. It shoots as good today as the day I got it.
Using a dacron string may be quieter on some bows, but IMO tuning plays a much larger part. If someone just likes dacron, don't see any reason to not use it. Just don't want to see the other materials get a bad rep. when they haven't earned it.
Chad