An interesting point you raised. Now allow me to the liberty of extrapolating it a little. Say if I use a very nice DX lens, like 17-55/2.8 and attached it with an TC1.4 to D800. It becomes effective 24-77/4 lens. Will it produce theoretically better image than 17-55/2.8 with TC, assuming at 1.4 Mag no IQ degradation?