A fed-funds rate that could end up as high as 6%, a level which hasn’t been seen in more than 20 years, is beginning to be seen as an outside possibility by some investors — bringing with it the risk of another painful round of selloffs in government bonds like the one seen this year. That’s one of the potential outcomes being entertained by some in financial markets, even though it’s much too soon to say if the Fed will ever get there: Policy makers won’t deliver what’s expected to be their first aggressive rate hike of the current cycle until next week.