I went through a similar decision process that you are, but then I bought a 5D for a short period of time. I ended up selling it and buying the 7D and never thought about it again. It is only with the 5DIII that I have even contemplated going back to full frame. I really didn't see a "need" for 8fps or any of the advanced AF features on the 7D until I bought my Sigma 70-200 f2.8 EX DG OS HSM and my daughter joined the color guard in marching band. The difference is simply incredible. 8fps with back button focus and the DOF preview button reassigned to Servo AF is just awesome. I can't tell you how often the difference from an OK shot to a great shot in sports is just a fraction of a second. With the custom user settings I can set my camera up for sports on C1, and setup a completely different group of settings on C2 for portraits. Also, when the light gets low, an f2.8 lens activates the higher sensitivity sensor on the 7D. That same pair as I pointed out above just nailed AF almost instantly at my daughter's sweet 16 party and it was a gymnasium at night lit only by a DJ booth.
Don't get me wrong. Full frame has its place. If you are printing really big, shooting a lot in low light, or shooting landscapes that require a wider field of view, they are nice to have. If you have an obsession with creating the most background blur possible, then a full frame will give you about a stop and a half more for the same focal length/aperture combination because the wider field of view causes you to have to be closer to the subject. But frankly I feel that the narrow depth of field is often over-used.
Don't take my word for it though. See if you can borrow or rent one. Try it out.
I am serious....and don't call me Shirley.
Canon 7D and a bunch of other stuff