Duobinary formats are today considered as being one of the most promising cost-effective solutions for the deployment of 40 Gb/s technology with direct detection on existing 10 Gb/s WDM long-haul (metropolitan and core) transmission infrastructures. Various methods for generating duobinary formats have been developed in the past few years but to our knowledge their respective performances for 40 Gb/s transmission have never been really compared experimentally. Here, we propose to evaluate at 40 Gb/s their respective robustness with respect to the most stringent transmission impairments, namely ASE noise, chromatic dispersion, polarization mode dispersion and nonlinear effects. We demonstrate that, owing to its enhanced resistance to intra-channel nonlinearities as compared to non-return-to-zero, duobinary can permit to reach transmission distances compliant with metropolitan and core applications on G.652 standard single mode fibre when quasi single-channel transmission conditions are met. We show furthermore that shifting optical duobinary filtering from the transmitter output to the receiver input can be of high interest to improve further the system maximum reach. We show also that phase-shaped binary transmission (PSBT) formats are fully compliant with 50-GHz channel spacing and that they are, in terms of transmission performance, as good as partial differential phase shift keying (Partial-DPSK), which is considered by equipment suppliers as the preferential transport solution for deployment of 40 Gb/s technology with direct detection on existing 10 Gb/s WDM metropolitan and core transmission infrastructures.