No, 5k is only a super 35mm sized sensor, for Imax you would want much more. That's why they are bringing out larger sensors (like the 28k!)
Imax is shot on 65mm film stock by the way. A lot of movies are blown up to this, but some are specially shot. For The Dark Knight, portions of the film were blown up from 35mm and some were shot specifically on 65mm.
The maximum that's currently being digitally projected at the moment in cinemas is 4k. Most digital cinemas are doing 2k. But even so, the more you begin with the better the downconvert will be. If you want great 2k, shoot 4k...