I guess my setup is actually very similar to yours. I posted in my question on this forum my room dimensions as 13x24, but actually, like yours, the back wall of the LR is a 4' wall bordering the kitchen/DR, about an additional 15' long.
To make it more complicated, the LR has a slanted cathedral ceiling, with the Left wall being 8' tall, and the Right wall more like 25' tall. Ian, (or others) does this change the recommendation as to M60 vs. M80? And are there any adjustments to be made to accomodate for odd acoustics from the roof?
And thanks for the hint, my receiver actually doesn't handle 4 ohm speakers, so I'll need to upgrade for sure.