In previous work, we presented a link quality metric for adaptive modulation and coding of two standard telemetry waveforms, orthogonal frequency-division multiplexing (OFDM) and shaped-offset quadrature phase shift keying (SOQPSK). That metric unified error vector magnitude (EVM) and Godard dispersion, for OFDM and SOQPSK, respectively, in the contexts of additive white Gaussian noise (AWGN) channels. In this paper, we present an alternative metric based on low density parity check (LDPC) decoding iterations. We show this new metric to be an equally effective substitute for AWGN channels but also to be applicable to a wider variety of channels, including those with multipath and interference. Furthermore, we show the metric to be robust within sub-optimal, lower complexity receiver architectures.