MGiddings Photography wrote in post #9975555
Low light 5D Mk ii -------- Sports 7D
Ditto... I use both.
But to expand a little:
5D2 - very low light, portraits, architecture, landscapes, studio work, wide shots, stitched panoramas, tilt-shift lenses, maybe even macro. Any slower paced shooting situation where max resolution, lots of enlargement, loads of fine detail are needed. More ideal for wide lenses.
7D - low light, faster handling camera for fast moving situations (AF speed and tracking moving subjects, primarily), sports, news, any action situation. More ideal for tele lenses.
These two cameras compliment each other pretty well in some respects. They share batteries. Their controls are in the same places (the 7D just has a few additional controls).
I'd never call one better than the other. They are designed to serve different purposes.
And, when it comes to actually using the cameras out in the real world, the 5D2 and 50D have more similar AF layout and controls, menus and such (but have somewhat irritatingly different button layouts).
Incidentally, your EF-S lenses won't fit on a 5D2... But the Tokina 12-24 will. And it will work to about 18 or 19mm without significant vignetting (don't even try it any wider, though... I don't know if the lens' rear element might interfere with the camera's mirror). A wide prime, like the 20/2.8 I use, is better corrected than the for WA effects such as barrel distortion, but it's nice to be able to use the 12-24 "in a pinch".
If you shoot very much action - be it BIF or sports or whatever - the 5D2's slow to acquire and reluctant to track AF will leave you wanting more.
If you are short on budget, but still want to combine formats... the 50D is a very good substitute for 7D. Having used a pair of 7D since November and with around 12,000 clicks on them, I have to say that unless you really need some of the other features unique to the 7D (video, for example) the 50D can handle it. 7D is good for about one more stop of high ISO usability. But I got much more consistent focus accuracy with 50D (I'm still experimenting with all the different 7D focus controls, trying to find a setup that works well for me). There's not a lot of difference between 6fps and 8fps. Either one fills up memory cards and hard disks in a hurry, when combined with a 15MP or 18MP camera. Spot metering on 7D (and 5D2) is a lot finer than on other current EOS model. 7D's viewfinder is the most usable one I've seen on an APS-C camera to date. 7D's "hair trigger" shutter release is more like those on 1-series cameras and takes a little getting used to, compared with either 5D2 or 50D.