If you are considering full-frame sensor body like 5D Mk II and Mk III, you also need to consider will my current Canon lenses work with them?
If they are EL-S designation, you can only use them on crop sensor bodies such as 7D, 60D (50D) and Rebel/Tx series. They will NOT work on 5D. Only EL lenses will work on both crop and full-frame sensor bodies.
For your stated purpose, 5D MkII will work fine; it is however, old by DLSR standards as it came to the market at the end of 2008 and your concerns are valid. That is the criticism leveled at 5D MkIII by the photographic community that Canon did not do enough in updating MkII. I think it is an unfair assessment overall as I think MkIII is an excellent camera, however, it is not worth $500 over its rival Nikon D800.
Canon did definitely improve the focusing system by borrowing the AF system from their flagship 1DX and made a host of other improvements to MkII. Still, people are not convinced that it is worth nearly $1,500 in cost difference over MkII. I do agree that $1,500 difference is steep but MKII's original announced price at the time of release was $2,700.
Maybe you should think out of the box and wait for the release of a new full freame sensor body if you are not in super hurry to upgrade ..... from NIKON.
Yes, Nikon; they announced that they are releasing D600, a ful frame sensor body rumored to be around $2,000. it would have Nikon's latest technology and is $1,500 cheaper than MKIII and cheaper than 4 yr. old MkII. And Nikon has all types of lenses that Canon has in their lineup.
Just curious what Canon lenses you have now ... if it is only a couple of lenses, and especially if any are EL-S designation, then swiching might be more practical than you think.
