Hi sedwards. A word of caution, judging yourself by the standards here is a tall order. There are a lot of really talented folks on this site that have developed all aspects of their craft. This includes lighting, composition, motion, post processing etc. What is it that you feel your pictures are lacking? I recently upgraded from the 70-300 IS to a 70-200 2.8, and the leap in build quality is significant. I now have the benefit of a fast, fixed max aperture. As you would expect I also noticed an increase in sharpness and contrast, especially when comparing images taken at the long end. That said, gains in this area are a matter of perspective. As people here have said before, after a certain point large sums of money will translate to incremental gains in quality. There are many shots from the 70-300 that I am still happy with, and in the grand scheme of things there probably aren't too many folks that could spot or care about the printed differences at equivalent settings. I think you'll love the step to L lenses if you stick with this hobby, but I recommend spending some time first thinking about what it is you don't like about your shots if you already haven't. If you can answer that it will be easier to pick the right gear. Also, and I apologize if you have a lot of experience with your 75-300, but note that without IS you need a relatively fast shutter speed to stop motion blur at the long end of that lens, roughly 1/420 or higher. With a narrow 5.6 aperture this can be difficult to achieve without bumping your ISO to higher levels. High ISO or a shutter that is too slow can lead to less than stellar image quality.