This is final stage before the version of GPdotNET v1.0 be released. Almost all planned features where implemented, and additional testing will be implemented during next days. You can download a new version of the GPdotNET v0.95 at http://gpdotnet.codeplex.com, as well as corresponding source code.
Regarding the parallel processing some improvements is achieved, but it depends of various parameters. For every different GP parameters, you can get different processors time. The screen below shows one example. The GPdotNET is consuming about 90% of Quad Core processor.
Some benchmarks where performed with other similar tools, and give very interesting results, but this is not official, and it is not quality benchmark.