I have not skied on the K2 but have a pair of 78's.
I am similar to you, mid 40's 190lbs and have always skied on race or near race skis.
Maybe it's my age but I am starting to enjoy skis more forgiving lately.
Because of my connections at our area I have several pairs of Head skis, the Magnum, the M82 and the M78 and the 78's are becoming my favourite ski for around here.
I originally tried them with a demo binding and thought they were weak, but with the railflex binding it is a completely different ski, much more stable.
With the sidewall construction they are torsionally stiff and hold on ice, but still allow you to ski in slush etc. I dont think they would be great in deep powder but deep powder around here is 3 inches.
I find I can ski all day without straining my knees like I do on the magnums and I actually find them more stable than the magnums.
Take this for what it's worth, you really have to demo because everyone has a different opinion and there are a lot of those here. I am skiing these in a 171 cm and I see no reason for longer, I have skied the 177 and unless I was out west I wouldn't bother. I have a 183 M82 for that. I find on these forums everyone says buy the ski long, and I wonder the motivation of that sometimes. I dont need to prove anything by skiing on a long ski, I did that for 20 years and I enjoy the shorter ones more.