I have seen people playing happily and successfully in that hole at pretty much all levels. If you are going down there and if you are into river running in addition to playboating, you should be advised that over 700 cfs, the run below the hole to the Mt. Evans exit takeout on I-70 is probably one of the best "bang for your buck" runs in all of Colorado. It is good at lower water too, but above 700, it gets "really" fun.
90 minutes to 2 hours of intense almost continuous Class 4/4+.
There is also a section near the end before the Outer Limits rapid that has several excellent surfable features. I just learned recently that some locals down there call it surfer's alley (or something like that).
As far as a more specific answer to your question, I can personally confirm that the hole is playable between 400 and close to 900, which is the range within my experience.
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