dug, I am having a similar problem. CopyToDVD will not write my 4x DVD+RWs ar 4x either. My problem is slightly different from yours, however because it will write at 2.4x (as opposed to yours writing at 2x).
I first tried with CopyToDVD 2.2.6 and it wrote at 2.4x. I changed the maximum DVD write speed (in the CopyToDVD settings) from "Max" to "4x" and I got the same results. I then went ahead and downloaded version 2.2.10 (I never upgraded before because I had no problems) and installed. I get the same results when set to "Max" so I changed it to "4x" and I get the same thing.
Although I am using the same kind of media as you (Memorex 4x DVD+RW) this has to be some kind of bug with CopyToDVD, because both DVDDecypter and Nero burn flawlessly at 4x on these Memorex discs. Not to mention, DVDInfo also reports these discs as 4x. Check my old post here. Perhaps a bugfix or update is in order for this software. I am using a Sony DRU-510A, so I also don't think it's a Lite-On problem. Anyone else having this problem?