I think the full grade as double is accurate. the 22k vs 29k at 1.66 has a logical answer, plus all kinds of unknowns. if a C+ is really a 2.49 and a B is a 2.84 (worst case ends of their respective prestiges), the advantage is about 1.1 (2.84/2.49) instead of 1.66 - the unknowns (at least I don't know them) are the timing of the offers, the starts or minutes in the offers, the actual value in the offers (makeup of CV,HV, evals, etc, not all are equal) and any other intagibles. That is assuming both are the exact same distance away.
ONe other thing I would clear up, prestige does work the same way in d2 / d3, but the money spent is usually so small, that large amount of money spent can kill the ratio's pretty quickly (2k vs 9k kills any ration edge one may have, 22k vs 29k not so much, but both are 7k differences)