nope, the Mk3 does not offer me anything I dont already have ;-) better ISO capabilities - perhaps and a more capable focus system . . . but the entrence price is not justifiable since my MKII produces more than exceptional work in low light with my glass ;-)
http://www.pbase.com/codyconway/imag...740/medium.jpg
Northern Caiman Lizard, Napo Amazonia, Ecuador, 5D Mk II, 500mm F4 IS L, handlheld standing in a canoe just after sunset. Printed this in 36x24 and have it hanging in my reptile room - Mk II or Mk III would've have mattered. The results show well.