This work explores the relationship between L2 proficiency levels and certain linguistic features through experiments in automatic proficiency classification. We use L2 Spanish and L2 Portuguese data and perform monolingual and cross-lingual experiments. We also compare native and leaner Spanish texts. To the best of our knowledge, this is the first work that performs automatic proficiency classification for L2 Spanish, as well as cross-lingual proficiency classification between L2 Portuguese and L2 Spanish. Our results for L2 Spanish are similar to the state-of-the-art, while our cross-lingual experiments got lower results than similar works. In general, all the experiments suggest new insights about the relationship between linguistic features and proficiency levels in L2 Portuguese and L2 Spanish.