I have this vertex array of a cube
float vertex_coordinates [] = { -12.43796, -12.43796, 12.43796, -12.43796, 12.43796, 12.43796, 12.43796, 12.43796, 12.43796,
instead of (+-)12.43796 use (+-)1
then apply a glScalef operation on your modelview matrix of 12.43796
I doubt this would speed up your code, however. All it will do is reduce your vertex array to half of its original size.