I used to divide the screen into 4 sections and have the 2D directly above the DI so I had both representations of the fish. What I found over time is that I was really referring to the DI image to interpret what I was really seeing in the way of fish. The 2D was just taking up screen space and wasn't really providing any value. I find much more value in having the SI full width so I can detect even smaller groups of Stripers off to the left or right as I'm trolling and adjust my trolling grid accordingly.
As Wayne said, I always have my depth displayed on the data portion of my screen so I always know the depth... whether trolling or at high speed. In my case, I have my transducer on a pontoon and can usually still get my DI and SI readouts even at 22MPH. I definitely get turbulence on the left side of the SI image since it is on the other side of the motor but it does work.