Canon G2X

Yes, by higher sensor efficiency I mean lower noise at any level.

Yes, by better sensor quality I mean, color, sharpness and fine detail.

So from what I can tell from your reply would be that a 10-15% increase in efficiency in either the G1 X or the G15 sensors would not make an appreciable difference in IQ. That is a very interesting  opinion you have. I guess we will just have to agree to disagree on this one subject. :/