Fell off this thread but wish I saw this. Those deepwater pumps are ridiculously awesome. I'm sure you'll be fine with the 10, but I would have suggested the slightly bigger one, just because you can turn it way down. The controllers are great too.The current pump is a Dolphin Amp Master 1/15 HP pushing 3500 GPH. The replacement pump is Deepwater Aquatics BLDC10 DC Brushless Pump. The detailed reader will notice that I'm replacing a 3500 GPH pump with a 2650 GPH pump. I'm doing this because I currently dial back the pump using valves, quite a bit, too. I can spend less money on a more energy efficient pump by buying a pump with a lower flow rate. Well, at least that's my thought process.
And, you're right about the fitting. The plumbing was designed for this so it won't be too bad.