Dual Wield R-Type

Apparently, the Dual Wield with R-Types do stack up, so at 2x +6 weapons will give +82% additional crit damage that stacks with the 150% with rank 1 crit. If that's the case, what's the break even point?

That's what the "Dual Wield (Single Hit Base)" column is based on. So use that column, but instead of comparing it to your stat sheet, compare it to your Base + Weapon 1 + Weapon 2, like is used for single hit skills. In essence, you actually need a lot less base damage for R to be effective with dual wield.

What would be the breakoff point? Will you calculate it?

Like I said, the equivalency point for dual wield is in the "Dual Wield (Single Hit Base)" column of the chart.