Well, first off I will mention if you are considering the 5D2 at all, or have intentions of getting something like it you may want to stray from the EF-S lenses (17-50 2.8). Maybe you are not like me, but I just hate buying things twice, I would rather buy one lens to fit a focal range that is going to suit me for years to come rather than go cheap on one I will "outgrow" soon after.


Other than that, I have a 7D myself and am seriously satisfied with it. I think they main difference will be light sensitivity, if you find yourself short on light with the 1.8's you already own, then the 7D may be your best alternative. On the other hand, if you really want the FF you could go for glass and save from work to meet your needs.


As for lenses if you choose them, rather than the 17-50 I would go for the 24-105L. If you are on the streets it isn't too menacing size-wise but makes for great shots. The quality is fantastic and the range is lovely too, plus you can go FF with it. While it may seem somewhat wide on a crop sensor, your Sigma will fill the gap, and once you get your 5D its range gets even sweeter.


Other then that I suppose it depends on your subjects, if you really don't shoot sports much then your 70-300 will probably suffice for now and I would focus on a more "walk-a-round" type lens.