The segmented contact method is used to study the performance of intrinsic and p-doped quantum dot structures emitting at 1.3 mum. From measurements of the absorption, it is shown that despite being doped to a level of 18 acceptor atoms per dot, only 19% of the quantum dot states are filled by excess holes, illustrating the importance of the continuum states in the wetting layer. We directly measure the modal gain and non-radiative recombination and show that the modal gain is increased as a function of transparency point when p-dopants are introduced without a significant increase in non-radiative recombination. These results explain the 65% reduction in threshold current observed for uncoated 1500 mum long devices at 300 K.