The stiffness rating of both racquets is about the same, but the increased weight of the n6.1 makes it the more stable racquet it seems. However, from what I've read some people seem to have arm problems with the n6.1 and people seem to blame it on the stiffness of the racquet. I have not read about arm problems with the RDS 001. I am demoing these 2 racquets and I like them both so I figured maybe it's better to get the one that's more arm friendly. Maybe it's the strings but to me the n6.1 feels a little more comfortable (recently restrung with SPPP) and I think the RDS 001 is strung with Wilson NXT 16. Any thoughts? Thanks for the help.