Delete this question please.
The United States today has economic growth rate of about 2 1/2%. This is historically low. The U.S. average from 1790 to 2014 was 3.73% according to this article: http://finance.townhall.com/columnists/danieljmitchell/2015/05/04/why-is-america-richer-than-kazakhstan-and-why-has-estonia-surpassed-croatia-n1993872/page/full
The fastest growing countries today are around 10%. Those are mostly poor countries, I presume it's easier to show a lot of improvement when you're starting from a low baseline. Among large countries, India and China are both growing at about 7%. The average for Europe is 1.4%. There are a number of countries showing negative growth, like Italy, Cyprus, and the Gaza Strip.
You could easily look up growth rates for various countries and project that forward 45 years. But that would be unlikely to give accurate projections: these rates tend to vary with all sorts of circumstances.
It certainly would be valid to look at historical rates to get a feel for what the standard of living might be in 45 years. If to get the standard of living you are projecting would require 20% per year growth for 45 years, that's very unlikely to happen. If you assume less than 2% you should be explaining why that country is stagnating.
As to who will be on top in 45 years ... of course one could speculate endlessly. I'd be surprised if a list of the major players was totally different from today, though it's likely some existing power will decline and some existing lower-tier nation will rise. Think how today compares to 1970, i.e. 45 years ago. Russia has declined sharply in power in that time. Besides that, any list of major powers is pretty similar.
On the other hand, compare 1935 to 1980. Britain and Germany were among the greatest powers in the world in 1935. Both were still important in 1980, but no longer the top of the heap. The U.S. rose considerably in that period. Etc.