I recently moved from the 7d to 5d mkiii. After getting used to the speed of the 7d, the mkiii is the least pricey way I was willing to move to ff. That said, the 7d is excellent. It is not as flexible as the mkiii regarding dof and low light photography to be sure, but is a great camera. I have shot it with many lenses. My opinion on the 17-55 is that it is a big lens. I bought the 24-70 because I knew I was going FF eventually. If I shoot a wedding, or event, it is great, but otherwise I usually put something else on the camera. It is nice to have because it is so versatile, but if I'm going to be in a more organized shoot, I will tend to use primes. My most loved lenses on the 7d were the 10-22 and 35L. The sigma 30mm is close to the L lens in output if not focus performance, but make sure you get a good copy. I imagine the sigma 35 is great, but all I own are Canon lenses. You will appreciate fast primes more on a crop sensor than on a full frame if you like the shallow dof and vignetted look. The 50mm f/1.4 is popular and the 85 f/1.8 is a good value too.