Does anyone have experience with these two cultivars of Calamagrostis? I recently bought a few 'Overdam' over 'Avalanche' (the 'Overdam' looked a bit cleaner, more boldly marked), but the little information that I could find on Avalanche has said that it is more vigorous than 'Overdam' - should I take these guys back and get the other cultivar? Any suggestions from those who have grown either or both of these plants? Thanks!