I hate powering down discs too much. They don't fly the same as intended (glide and fade-wise for me), and I don't trust it...so then I throw it badly.
That being said, my faster OS discs are an Xcal and Firebird. I will use the Xcal for 300-350' OS shots (Destroyer past that...the Xcal is too beefy for me to push far), and Firebird for 250-310' OS shots. I then go to a Verdict, which at Firebird range is pretty straight with a finish, but at 200-250 it will get pretty OS. That being said...I feel like this is almost too powered down for me.
If I were to try throwing an Xcal 250' it would cut through the air way too fast and fade a bit more. A Firebird is so OS, that if I tried to power it down to 200' it would just start fading out of my hand and I miss my intended line 90% of the time.
The more I've seen some guys I play with throw Gators on 150-250' shots and they do it consistently every time, the more I think that it's a useful thing to have. If I lived somewhere that was windier, I'm quite certain I would have a Gator or something in that class that is true OS.
So really, it depends on how your bag is set up (what speeds are your current OS molds), and how far you throw/how you feel about throwing discs at under 60% power. Personally I hate throwing discs that softly unless I have to for a putter upshot, and then it's a different form usually.