Isn’t it also unlikely that it is less than interest difference? If you believe that USD drops less than this difference, you should keep all your CHF savings actually in USD while this difference exists. (not my advice; too risky and don’t think you’ll win anyway)
Don’t forget that a fall in USD is likely to be correlated with a fall in USD interest rates so don’t expect the 4% differential to continue.
All my savings are invested in equities atm.