Gabby, it depends what you will be primarily shooting, and if you need the 5DmkII superior low light and high ISO performance, or the 7D fps and AF...its just a matter of which is more important.

The other thing to consider is your lens choices, and the 7D is a 1.6x sensor so your lens focal length is different to what it says, but if you take that into consideration when buying lenses it shouldnt be an issue.