Fabales is a cosmopolitan angiosperm order which consists of four families, Leguminosae (Fabaceae), Polygalaceae, Surianaceae and Quillajaceae. The monophyly of the order is supported strongly by several studies, although interfamilial relationships are still poorly resolved and vary between studies; a situation common in higher level phylogenetic studies of ancient, rapid radiations. In this study, we carried out simulation analyses with previously published matK and rbcL regions. The results of our simulation analyses have shown that Fabales phylogeny can be solved and the 5,000 bp fast-evolving data type may be sufficient to resolve the Fabales phylogeny question. In our simulation analyses, while support increased as the sequence length did (up until a certain point), resolution showed mixed results. Interestingly, the accuracy of the phylogenetic trees did not improve with the increase in sequence length. Therefore, this study sounds a note of caution, with respect to interpreting the results of the “more data” approach, because the results have shown that large datasets can easily support an arbitrary root of Fabales.