I would think that it is dependent on what type of filtration you are using.
If you was using a shower full of BHM then my understanding would be a very fast turnover rate seems to do the trick.
If you was using a more conventional type of filtration then you would not want to pump too fast as you would stand a chance of
1. Settlement not doing the job and ending up with a filter full of poop.
2. Not enough contact time with the bio and so the good guys cant do there work efficiently.
This is only my opinion as i have not really been keeping koi/water long enough but i am sure some of the very knowledgeable guys on here will help and correct me.....most probably
