An update:
The more I think about it, the more I think that a player's peak should be measured in years, and not by number of innings. The amount of cricket played varies considerably from the beginnings of test cricket to the current era. A batsman in the modern era could play 40 innings in 2 years, whereas George Headley played 40 innings across 24 years.
But, how do we measure a five year peak?
The simple way is to just do the best five calendar years of a player's career. However, what if they miss a year? What about the war years when no cricket was played? Denis Compton peaked from 1937 to 1948. Do we only about 1946-1948 as his peak? That is only three years. Do we just do five calander years and call it as 1944-1948? That would be strange as obviously he didn't start playing cricket again until 1946. Or do we cut the war years out altogether? That sounds more reasonable.
However, what about Clyde Walcott? He peaked from 1952-1956 in terms of five calendar years, but he didn't play any test cricket in 1956. So his peak was only really 4 years (1952-1955). What do we do then? Do we take 20% off his peak rating?
What if Walcott happened to miss a year in the middle of his peak, for example, 1953? What would we do then, as he was again only active for four of the five years of his peak period.
How about five calander years in which a player was active? For George Headley, that would give a peak of 1930 to 1939 since he was only active in 1930, 1931, 1933, 1935 and 1939.
I have no idea what to do. I would appreciate any thoughts. Cheers.