While infrastructure providers are expanding their portfolio to offer a sustainable solution for beyond 10 Gbps in optical access network segment, we compare experimentally several alternatives that may be used in future passive optical networks (PONs) to deliver 25+ Gbps net-rates. As promising candidates, we consider the intensity modulation direct detection (IM-DD) systems employing the following modulation formats: (i) duobinary, (ii) 4-level pulse amplitude modulation (PAM4), and (iii) discrete multitone (DMT), which are all more bandwidth efficient than the non-return-to-zero (NRZ) in current 10G PON solutions. In this paper, we focus on the optical budget after transmission over a 20 km single-mode fiber (SMF) link in C-band and discuss the intrinsic imperfections of optical components that may significantly reduce the received signal quality.