I just did an overlay of two 300 profile photos I found on e-bay. One was the 300 sel and the other a 300 se. Here's what I came up with.

The two cars are virtually the same length b to b. The differance is the 300 sel has a longer rear door and the rear wheel is set back closer to the rear bumber. The gas filler door is set back as well. The C pillar may be a little narrower as well on the se. So it appears that the 300 sel just has more leg room without compromising the trunk space.

Thanks again for pointing me in the right direction.