I look at general head pressure of smaller pumps cutting my flow in half from the pump rating, sump to DT. I used a Mag 7 on my RSM 250 return for a long time.The Mag 9.5 will work, I think they have a 3/4" output on them they are beast pumps & much bigger than the 5 or 7 so you need to think about the body size in the return pump chamber area. I understand the 90s at the top getting over the lip, do you need the 90s into the sump? Your useing a "Y" for your return, why not a "Y" into the Sump/Fuge on the overflow side? Also using flexable hose where you can really reduces your head pressures, I understand it's not as pretty. I think with either 7 or 9.5 your going to have your flow but using the calculator to be sure is best. My Vortechs have spoiled me, they are my flow, everything else just moves water where it needs to go. You could run one or two MP-10s in your 29 and never have to think about the flow. Have fun!