emonLib has not changed for quite a long time. When I last checked it - and there have been no changes that I know of since - the speeds with a standard emonTx are:
calcIrms( ) - approx 5588 current samples per second.
calcVI( ) - approx 2535 pairs of voltage & current samples per second.
This was published with a few more details and hints at Sampling rate of emonLib
emonLibCM is totally different, because while it samples each input much faster, it handles all the channels as a sample set (for 4 current channels reading V I1 I2 I3 I4) continuously; rather than V I1 for 200 ms, then V I2 for 200 ms, etc. Therefore, when reading 1+4 channels, the actual sample rate for emonibCM is about 1900 sample sets per second, against 2535 for just one current channel with emonLibDS (Discrete Samples). Everything about emonLibCM is in the documentation that comes bundled with the library in the download zip file.