Aside from everything already said, and assuming you can put the same lens on both cameras, you have to be sure that the in-camera settings on both bodies are the same; ie sharpening, noise reduction etc. It is likely that this is, in practice not possible even when all are set to zero. You need to dig in to the menues on both cameras and set things as near as the options permit to be the same. Having been through the CanonvsNikon for sharpness debate and having bought both systems to do this, I think there is actually little difference!!!!!!!!!

Aside from everything already said, and assuming you can put the same lens on both cameras, you have to be sure that the in-camera settings on both bodies are the same; i.e., sharpening, noise reduction, etc. 

It is likely that this is, in practice, not possible — even when all are set to zero. You need to dig in to the menus on both cameras and set things as near as the options permit to be the same.

Having been through the Canon vs Nikon for sharpness debate and having bought both systems to do this, I think there is actually little difference!