I don't think the RD30 is like 4 DDC's, more like 2 to 2.5, I have one and it was a little stronger than my dual D5's. The thing is that it has a lot of head pressure and with that amount of tubing it would be better than going dual DDC's. Not sure about the Dual D5 strongs, Martin seems to like those and that might be the ticket in this situation. You could always do two RD30's and separate your loop into two. Not sure if you have a budget for this or not.