Todd, I've been a fanatic about low speed planing since day 1, and my rig will plane at 12-13 mph with full load (~3900 lbs total boat + crew load; will email you my weight summary) @ 2500 rpm, exactly what I want. Just ask Snookerd, GFS, Skip or Carla, who have all ridden on my boat in choppy conditions. What it takes is trim tabs, a 4-blade prop, and maybe a Doelfin or equivalent. (I added the fin before I tried a 4-blade prop. May have to take it off one day just to see if it makes any difference.)
Here's a couple photos that should answer the clearance issue. This first one shows fore & aft clearance with motor at full tilt.
This next one is a better shot of clearance with transom . . . about 7.5".
My bracket has a 30" setback. From this picture, I'd say a 24" setback would work fine for a 150 E-tec. Don said he could make them in 18, 24 and 30" sizes. If you went with a 115/130 V-4 E-Tec, you might even be able to use an 18" setback; you should be able find motor height difference between the V-6 and V-4 from BRP website or from this great E-Tec owners forum
web page . Just looked at my 2009 catalog and it looks like they've gained weight since I bought mine, or else they've changed from quoting dry weight to wet weight. A 25" shaft 150 is now 433 lbs (mine was 427); a 25 115 is 390 lbs. I do know that BRP includes weight of the cowling. When you compare to a 4-stroke, make sure they include the weight of the oil and cowling!
Although I originally considered the 115,I've ended up so heavily loaded on some of my trips, I'm glad I went with the 150. Even with that load it gets on plane at less than half throttle! One other thing to consider is that the Seafari is a little less stern heavy than the CC's, so that makes motor weight a little less critical. Denny