The difference betwen the VX-II and VX-2 is significant if optical performance is important to you. From image contrast to edge-to-edge clarity, the newer models win hands-down. In low light, the VX-II could not resolve detail as well the VX-2, which to me is more important than many other aspects. Light transmission may be close and the sight pictures nearly equally bright, but that doesn't mean anything if you can't discern what you are looking at.
Regarding the comparison of Conquests and Leupold VX-II and VX-2s, if performed in unbiased fashion and in such a way as to render usable and valid test results, the Conquests grade out much higher. In fact, in many areas, the Conquests are ahead of the VX-IIIs The NEW VX-3 and the Conquests are pretty evenly matched.