I typically wear the Kenai over the 240 for convenience. If I'm wearing that combo, I'm not at the edge of the temp ratings for my gear. If I was cold, I would either wear the Kenai under the 240 of I'd more likely have a different jacket to wear over everything.
The older Kenai was sized better then the new vest, and cut similar to the 240. The new vest is quite abit larger and cut for heavier set guys. I should have gone down a full size in the Vest. My 240 is atleast a couple of years old, so dont know if they've changed the sizing on it.