Linearity: function's derivative is constant w.r.t. the parameter discussed. dT(K)/dK = -1.25/K^2 and this most certainly is not constant.
To clarify, the original title said that this was a method for _exponentially faster_ data transfer. That said, you got me in that it is not linear. As you have shown, that function is quadratically decreasing (which is _worse_ than linear). The title has been corrected since then, so I kind of got my point through.