Employing 8-bit 65GSps digital-to-analog converters with pre-equalization and Nyquist pulse-shaping, we generated a terabit superchannel based on both low-baud-rate Nyquist frequency-division-multiplexing (FDM) dual polarization quadrature-phase-shift-keying (DP-QPSK) and high-baud-rate Nyquist DP-QPSK signals. The 1.2-Tb/s superchannel transmission over 80100 km ultra-large-area fiber with effective area of 125 was demonstrated using erbium doped fiber amplifier only spans. We further discussed the roll-off factor in Nyquist pulse-shaping on the system optimization. It has been found that the Nyquist FDM DP-QPSK signal outperforms the high-baud-rate Nyquist DP-QPSK. Given the same data capacity, the Nyquist FDM DP-QPSK scheme exhibits better tolerance to fiber nonlinearities.