This reminded me of the 4 minute mile. The first 4 minute mile was a 3:59 run by Roger Bannister in 1954. Prior to that, the record was a 4:01 run in 1945.

A 4% improvement on the 4:01 would be a 3:51. A 3:51 wasn't achieved until 1966, about 20 years later.

So 4% can be quite a jump!