An ideal (minimal) 2.1 setup

Doesn't need a center channel, but needs a couple of subs.  If choice 1, a KEF KC62 would seem ideal -- Darko review.

I'm more interested in the distinct sound signature differences between the two.

To me, it's all about clarity and detail. You don't need a center channel, but do need a couple subs.

ET LFT-8s and really move up a big step. 

When you say movies do you want the loud theater type of sound? If so I think the kefs hight run out of steam even crossed at 80hz. Or at least struggle to keep up with the subs output at high levels. 
As for the Kef sound. The kefs have a very wide soundstage that still has good center focus and are very neutral. The down side of the kefs is they lack dynamics and the highs lack refinement to my ear. I have always passed on Kef when directly conspired to competitors of the same price. Tue LS50 might be the exception as they are pretty cheap for what you get. But at the Reference 1 level and up I would take different brands. Just my opinion.