This is of course my opinion, but I think you misunderstood, or is does for that matter, what he meant by the R series is the climbing bike. The R series is going to be a little lighter, due to it being a full carbon frame, as well as having a more upright position. The two properties make climbing a bit easier and more comfortable, but what AngryScientist said is what's most important, it's the engine that counts.
As far as being easier because of the weight difference, we're talking about 2lb or less. I can almost guarantee it will be easier for you to drop 10-15lb way easier and make WAY more of a difference than 2lb on the bike.