With a little simple algebra, it occurs to me that if x is the original ROR, in decimal form, and we're looking for the formula to express total ROR if we plan to siphon all profits, should we double, then the new ROR is just: 2x/1+x.

Correct, but you need parentheses in the denominator:

2x/(1+x)

Rather important parentheses, in this case.

ETF