How is OpenGL formed

is the switch from fixed rendering pipeline to VBOs & shaders a big one in terms of performance? Also will it be hard to comprehend coming from doing only fixed rendering pipeline methods?

Here's another question for you guys:

Would changing my GL_QUADS -> GL_TRIANGLES be faster in terms of fps or will it not affect the fps that much?

note this is all with the fixed rendering pipeline atm. Once i get this to its max speed then i figure i'd go into shaders and VBOs

thanks for all the help up to this point