Been using mediums for years on my 414ce with no issues. As I recall, I did not even need a truss rod adjustment. The guitars can certainly handle it.
I have strong hands and a fairly heavy touch, so I like the extra tension and extra sound output from driving the top a little bit harder. I often tune down too, so I started using mediums to avoid floppy strings. My latest string order was a few sets of Elixir medium-lights (medium on the bass side, lights on the treble side) just to have a few of those on hand. Sometimes I like the feel of lights too, especially if I happen to be working on new pieces and playing a lot of repetitions. Just so you know, mediums tuned down one whole step D-d have almost exactly the same total tension as lights tuned E-e.
