Oh, you wanted per capita GDP dates, too. Making some rough assumptions (e.g. both populations continue to grow at same rate — around 0.7% per annum — across the period), I get dates of 2062 and 2078 for 8 and 9 percent respectively for per capita GDP equalization. Of course, if China’s population growth rate slows, as demographers expect, while the USA’s doesn’t, or slows less, then the dates will be earlier, though only by 5 yrs or so.