with low light performance of the 5n, what is the appeal of full-frame?

I think differences are mainly DOF and extreme high ISO (>6400) performance.

Check it out yourself at: http://www.dpreview.com/reviews/sonynex5n/14

Note that a FF NEX will be a problem, because the NEX e-mount lenses will not perform well in the corners I guess.

Lenses will be bigger and more expensive.

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