It is not that strange that it is using 100% of your CPU. The resize actions are CPU intensive and Magick.NET uses as much processor power as it can get.
The next version of Magick.NET will include OpenCL support. This will move certain operations to the GPU instead of the CPU. But if your graphics card is not fast enough the CPU will be used. The first time your start Magick.NET with OpenCL it will measure the performance of your videocard and your CPU and decide which one is better. Adding a good video card or APU to your system might improve the performance.
The next version of Magick.NET will include OpenCL support. This will move certain operations to the GPU instead of the CPU. But if your graphics card is not fast enough the CPU will be used. The first time your start Magick.NET with OpenCL it will measure the performance of your videocard and your CPU and decide which one is better. Adding a good video card or APU to your system might improve the performance.