Debbie
Many thanks for the link that I requested for the RAW file. I'm afraid I can't improve things very much, for the simple reason that I think a lot of the fuzziness in the shot must be due to the weather. Looking at the trees on the far side of the lake at over 100% in the RAW, they look quite fuzzy and indistinct. I used CS5 and tried the noise reduction, which helped a bit. But if it's due to something in the atmosphere then noise reduction won't really help. That's why it looks painterly, as you said - the detail in the trees looks as if they have been brush-stroked because of the inability of the lens to more-accurately resolve the detail.
Re-shooting, on a better day would definitely improve matters. As would shooting at ISO100. You had lots of scope at 1/4000s to reduce the ISO. And f/11 rather than f/8 might give slightly better results - it depends on the lens.. Carry a tripod in the car.
I really do like the scene though - very tranquil. I think I need to relocate to VT - what with Katy's scones and views like this, it has to be better than Wales - low hills and stale Welsh cakes.