o switch off all light sources
Nonsense. Swtiching off lighting may speed up the rendering, but totally changes the appearance of the scene.
o convert the geometry into triangle strips and use vertex arrays
Correct. Triangle strips lead to decreased memory usage (see the Wikipedia article on them). The advantage of vertex arrays (one GL call per each vertex parameter per each larger piece of geometry) over immediate mode (one GL function call per each vertex parameter per every single vertex of the geometry) is the smaller number of GL function calls, which leads to less CPU and system bus bandwidth usage.
o use tri-linear texture filtering
Nonsense. Texture filtering defines the way in which “stretched” textures’ pixels are interpolated. Obviously changes the appearance of the scene.
o add a specular material property to all surfaces
Nonsense. This increases lighting quality and may lead to performance reduction rather than improvement. And, it changes the appearance. See the Wikipedia article on specular highlights.