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None of the bettors/raisers were overly aggressive...
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What does that mean? Does that mean that 3-bets = flopped a nut straight? Could it possibly mean two pair or an overpair? There are basically no realistic ways your set is a terrible underdog.
Here's your set against a flopped straight and a very live spade flush draw:
http://twodimes.net/h/?z=1190075
pokenum -h 5h 5c - 8c 6h - as 3s - 9h ah -- 9d 5s 7s
Holdem Hi: 820 enumerated boards containing 7s 5s 9d
cards win %win lose %lose tie %tie EV
5c 5h 256 31.22 560 68.29 4 0.49 0.313
8c 6h 323 39.39 493 60.12 4 0.49 0.395
As 3s 222 27.07 594 72.44 4 0.49 0.272
Ah 9h 15 1.83 801 97.68 4 0.49 0.020
Usually, you're not up against a flopped straight AND a flush draw. I'll let you visit twodimes and run those equity numbers for yourself.
I really hope this was a joke post...