These clusters change around depending on settings, so it is hard to compare them one-on-one since settings maybe different. This is the best autosomal study on Horn of Africans published so far:
http://journals.plos.org/plosgenetics/article?id=10.1371/journal.pgen.1004393
PS. Many Southwestern Ethiopians like Omotics and also the Gumuz tribe in Ethiopia are much more African than Somalis. So, no, Somalis are not the most African in the Horn. Only compared to highlanders affected by Semite migrations, yes, but not all of the Horn.