I would love to be in that location - it looks very inspiring and relaxing. Thanks for the image. It is a great image, but I would suggest using an 81B filter; it will add a bit of warmth to the image, and give the greens a bit more "velvety" look.
That is a mighty long lens for 4x5! Agree that more could come from the greens, but since it is a scan from colour neg, you might try removing some magenta, which would boost the greens and should make the sky a stronger blue. You can do this in a number of ways but adjusting the green curve is probably easiest. Obviously this is something which you could play with when making the print. I find it very hard to get convincing colours straight away from scans of colour neg film.
An inverted warm-up grad filter works well in a shot like this. Hereby the sky is left colder and the rest gets warm-ed up thereby enhancing colour contrast. Mine is an 81B with a soft transition which I feel works well when there is haze on the horizon.
I have 2 81b's for my lee holder. A.3 hard grad, and a .6 soft grad. I never thought about using it upside down. Doh! It was late in the day and was already taking on the sunset colorcast, more than shows in the scan. I thought it would be warmer looking than it was. My fingers were freezin, it was only 34 degrees. After Roteague's coment I put an 81 warming filter on it in PS, and it looked much better. As I said I rarely shoot color. I might have to try some more after looking at Roteague's site, man that stuff is fantastic. Don't know if I will have it printed or not . I don't do color at home.