OpenGL is only a specification, is a good specification, but the bigger problem is how is implemented, the same as for DirectX. The current implementation of OpenGl and DirectX is so badly done on Windows that is very and very slow that you will need a powerful graphic card processor to help with the speed. With the current CPUs any well written software rendering engine will be very much better and faster than any super video card with OpenGL or DirectX, but today nobody does it anymore. This was the reason why I've created my own engine (PropViewer and ArcMaker in freestuff/marketplace).

Stupidity also evolves!