I agree with MillerKid, 10-12x is typically what I understand for reef tanks, not really required/desired for most freshwater (although I know some folks prefer that here).
In my experience the limitation that I have is not with the pipe size and actual drain, but the rate of how much water can flow into the overflow. Short of cutting the overflow teeth (which I don't think it's worth the effort in my case), I've adjusted my return pump AND water return direction as to not flow against the overflowing water and better balances between drain and return - if that makes sense LOL. I use only 1" drain standpipes (Herbie method, but with a third dry stand-by taken from Bean Animal). I call this out, as it will be something you'll need to consider if you want to get high turnover as you are looking for.
Anyway, keep in mind with the sump you suggested above, you are looking at ~300 gallons of water. I think there are a lot of DC pumps out there to chose from. I'm using Waveline 10000 II for return and 12000 for closed loop circulation pump. On paper they are ~2800 gph and ~3200 gph, respectively. You also want to consider head and reduction in flow too. I like DC pumps since you can adjust. The Waveline aren't the best by any means, but for the price and flexibility, I'm been happy, so far. Not to mention they are very quiet.