DX11 render to texture low-framerate

There is a 70% percent framerate drop when using the DX11 MRT/TempTarget renderers to render a texture out to another quad and renderer. When getting the texture from a the standard DX11 renderer, the performance is much higher (using the same resolution). For the performance tests, I simply scale the standard DX11 renderer window to size of the preferred target texture renderer size and it passes the resolution to the texture. However, I need to set the texture resolution manually, but there are no Texture SizeXY Pins in the standard DX11 renderer. Any ideas how to define a texture size in the standard DX11 renderer or how to achieve the same high performance in the DX11 MRT/TempTarget renderers?
Thanks for any suggestions!