Having difficulty selecting ISO on 5D classic.

Recently opted to sell my 40D which I enjoyed and purchased a very clean 5D.  The reason was to take advantage of a full frame camera for wider landscapes primarily. I primarily use the 24-105 with it.  I often keep it in program mode and unlike the 40D, I now have to select ISO.  I use pretty basic rules.. sunny outside 100, cloudy outside maybe 400-600.. indoor no flash 1600 and hope for the best..  My first observation was the 5D screen is pretty much worthless, often casting a green hue over most of my pictures.  Overall, the pictures don't appear as crisp as those I took with my 40D... maybe I just need to use it more and get a better taste for it.