For Conneaut I personally like it around 250-300. To be honest I don't really pay a whole lot of attention to the Conny gauge so I'm not really sure what the max would be, but I remember fishing it one day last year when it was getting into the mid 300s and blowing out. Someone correct me if I'm wrong on the numbers. I've fished it at a whopping 50cfs before and it still had a much better flow than the PA tribs usually do lol.
I don't have a lot of experience steelheading the Grand as every time I want to fish it it always seems to be blown out. It takes FOREVER to clear! Sometimes a week or more. If that's the case you could always check out the tribs, or head to the Chagrin, Ash, etc. Anything around and preferably under 500 and you should be good.
Edit: Post 1000! lol