Early Morning Lake Landscape - How to get a more balanced shot

[alextdel]

I have been trying to get some landscape shots at Hinze Dam (Advancetown Lake). I'm aiming at a large print.
I'd love any advice on getting a better shot. Mine are always too dark despite the histogram looking pretty full to the right.

To take this one I put on an ND 8 to soften the water and a soft NDGrad to pull the sky down. Sun was to my left. It was about 20 mins after sunrise.
ISO 100
21mm
f/13
5.0sec
In Lightroom I have pushed the exposure up about 1 stop, pulled the highlights back and selectively put some saturation in the cloud and the reflected cloud using the adjustment brush

Advancetown Lake1-1.jpg
the histogram looks like

Histogram.JPG

This on was taken earlier with no filters
ISO 100
19mm
f/11
4sec
Advancetown Lake2-1.jpg
with this histogram
Histogram2.JPG

What do you think??

This was my first outing with my new 6D