In this paper the influence of LO spurs on the transmission performance of an E-band analog front-end is presented and compared to theory. A novel measurement setup is introduced to generate LO signals containing spurs with adjustable spurious tone frequency and suppression level. In the presence of variable LO spurs, broadband QPSK signals with data rates of 1, 2 and 6 GBd are transmitted. The received signal quality is evaluated in terms of phase noise and error vector magnitude (EVM). The received signals show a EVM floor of -18, -17.5 and -12dB for data rates of 1, 2 and 6 GBd respectively. For all data rates, the error floor is reached at a spur suppression of around 40 dBc.