I use quantstrat
Kevin —I believe you would agree that it is always better to be approximately correct than precisely in error...JK...That's not the only issue. For Portfolio A, all instruments are expressed in a common unite of account (USD) and have the same risk-free rate, and probably also have synchronous closing prices and holiday schedules. For Portfolios B and C, even if foreign market closing prices were available, without contemporaneous closing FX and 1-day forward rates, and adjustment for non-synchronous closes and holiday schedules, your historical Sharpe Ratio will be both inflated and inconsistent (spurious).