Are you using the Radeon drivers from ATI/AMD or the default drivers installed by Windows 8?
My guess #1 is that the OpenGL 2 support by the drivers which you currently use is bad/broken.
Normally an i5 and 8GB should be more than enough to run Godot fluently.
Does the performance in the Godot Editor differ when you switch between 2D/3D and Script mode?
Another issue could be when you use a custom shader with very bad coding/performance. (Doesn't look like that in the screen shots). Because shaders are also shown in the editors 2D/3D preview.
Guess #3 is that your notebook in general is performing badly because of other problems. But you should know that. ;-) You could check the task list to see if one or more cores are at 100% and some notebooks also speed down when they overheat (i.e. because of too much dust in the fan).