Well yesterday I was out on my 8'7 Flow in knee high mellow waves, and that was great fun. So slightly bigger conditions today so I took my Speeed 8'10 and Shroom 8'3 along to put side to side in same conditions.
The Speeed had the speed, lovely mellow ramps and great stability and fast enough to pop out front and carve a neat bottom turn then floater to nice drop in and hard backside carves.. all a great deal of fun.
The Shroom was more a pivotal slash/burn ride, the take off was really stable and the drop in floaty, then the bottom turns were a little pulled in so I had to make the best of the wide tail to carve some slashy turns.
In mellow waist high with shallow ramps the Speeed has the edge, because of the speed. It just takes off and creates space and time for you to think about what you're going to do when you get out front.. left/right/slash/turn..
The Shroom will do all of this and is more manoeuvrable but stays in the pocket and not out front, so carves need to be tighter and slashy.
I have a break 700mtrs from the beach on a sand bar, the paddle over is often across a rip and both boards paddle over this admirably, the Speeed a little quicker probably because the length and width, The Shroom a little longer but really stable because of the length and width.
I love both, well all three, they are fabulous boards and yes I do often feel a cross over in some conditions but I chose them for thier ability to take on all conditions and I choose one just basically on the day and head to the beach.. the only time I'd definitely choose the Flow is when it's shoulder + and sucky.. but then I take that out in knee high mush too..
Flat Water cruising, not that I do much of that, I'd choose the Speeed every time.. In fact at my sailing club we did some racing around some bouys in a mini series and I used the Speeed.. it's just a little quicker and easier to paddle in a straight line.. it's still a wave board but it goes well in flat stuff.
Note: I bought my Speeed first, then the Flow and then the Shroom.
Choices eh.. oh the dilemma.

Does this help?