Macro photography where maximizing depth of field is desired is one of the few areas of photography where a larger sensor can be more of a disadvantage than an advantage:
You'll get narrower depth of field with a larger sensor than with a smaller sensor when shooting at the same reproduction ratio.
Most such macro photography requires total control of the lighting anyway. It's normally much easier to provide more light to overcome the signal-to-noise ratio disadvantage of a smaller sensor than it is to deal with the additional diffraction caused by using a narrower aperture to get the same DoF with a larger sensor.
For more, please see:
How does sensor size impact depth of field and diffraction for macro photography?How does sensor size impact depth of field and diffraction for macro photography? Note that the answers there assume constant lighting conditions between the two camera/lens combos.
Macro with crop bodyMacro with crop body
How do I choose a camera for macro photography without considering special lens?How do I choose a camera for macro photography without considering special lens?
How does focal length relate to macro magnification?How does focal length relate to macro magnification?
Why are macros from my new DSLR no better than those from my P&S?Why are macros from my new DSLR no better than those from my P&S?
