Well, if you make the math, Yami Bakura lvl. 40 costs DOUBLE the dices as lvl. 30. So if we follow your chart, assuming the Dices to Points radio.
6000 x7 =42,000 x 2 = 84,000
7000 x7 =49,000 x 2 = 98,000
2000 x18 =36,000
3000 x18 =54,000
Still makes it more effective to farm Lvl. 30.
Maybe I'm doing something wrong, but I've tried that deck several times and haven't won once. I think I'll stick with my lvl 30 farming deck, which has been able to get around 9K consistently. 2 rounds of that isn't much lower than what you got for the same amount of dice, and it's a lot easier IMO.