Important new R1a SNP was discovered recently - Z280. Unlike R-M458 which is more common in Western Slavs, this SNP appears to be predominant among Eastern Slavs. It is also added to ISOGG tree: Y-DNA Haplogroup R and its Subclades
I guess this new subclade should soon help us in getting some answers we've been looking for lately. It will also be interesting to see how frequent are those subclades bellow R-Z280.