For fast link adaptation (FLA) algorithm, link quality metrics (LQMs) are presented for IEEE 802:11n WLAN systems with convolutional coding and higher order modulations. The LQMs estimate the PER of an instantaneous fading channel such that the FLA technique can dynamically select a suitable modulation and coding scheme (MCS) which fullls a PER objective. The presented LQMs are Raw- BER, EESM and MIESM, and MMIBM which utilize the post processing SINRs to compute the uncoded bit error probability, effective SNR and mutual information, respectively. We also present a novel LQM, MMIRM, which is derived from the reliability of the generated LLRs and it can be useful when linear receivers like MMSE are not employed. However, more research in MMIRM has to be carried out to bring the performance up to the same level as the other presented methods. We also give a useful upper bound of the performance of any fast link adaptation scheme which is obtained by simulation. It is shown that the best LQM achieves a throughput that is at most 1 dB and 1:25 dB from the practical upper bound in SISO and MIMO systems, respectively.