There can be a very noticable difference in 10-15 watts if the lesser of the two has a very different power supply. I found this quite apparent when I went from my former Marantz 6200 to my current 8300, which is only a 15w difference, but let me tell you the difference was immediately noticeable. There is about a 10lb difference between the two because the 8300 has a much larger power supply and it showed.
If it were me, I would go with the 2807 simply because it has better HDMI capability which would presumably serve most better going forward.