So I looked at where some players (probably not a very scientifically selected group) ranked at early and late stages of their careers. I tried to find periods that parallel Pujols so far. But I was not always able to. In the table below, I either divided a players career roughly in half, or did the first 8 years and next 8 years 9since Pujols has 8 years so far). Then I also simply used when a guy really started to dropoff as a dividing line. The last 10 lines are all power hitting 1B men. Those guys I found by getting the top 10 all-time in SLG relative to the league average with 5000+ PAs using the Lee Sinins Complete Baseball Encyclopedia. That should give a group that is like Pujols (Greenberg and Mize don't appear due to WW II gaps).
Then I found each guys offensive winning percentage (OWP) for the given period. OWP is a Bill James stat that says what a team's winning percentage would be if it had a lineup of 9 identical players who all hit alike and they gave up an average number of runs. Since I got the data from the Lee Sinins Complete Baseball Encyclopedia, it is park adjusted. I also found where he ranked all-time for the stated years or up to a certain year. The normal PA minimum was 5000. But if a guy had, say, 4900 PAs in his first 8 years (or whatever the time periods was), I used that for both periods shown.
There is quite a variety of outcomes. Some guys fall quite a bit in the rankings due to a much lower performance in their 2nd half. Some actually did better and rose in the ranks. So based on this, where Pujols ends up is not clear.
I also took all the players who had 5000+ PAs before the age of 28 who also had at least 2500 PAs from ages 29-36. Of the 75 players in the first group, 49 made it into the2nd group. Only 16 of the 49 had a higher OWP from 29-36 than they did up to age 28. Roberto Clemente was the one real big gainer, .162 (from .531 to .723). The average change was a loss of .030. Only 8 of the 75 guys from the first group had 5000+ PAs from age 29-36. It seems like the chances Pujols will even get 5000+ PAs over the next 8 years is low. But there might be something I am missing here.
The other thing I did was to look at the normal performance trajectory as players age. I found all the players who had 15+ seasons with 400+ PAs up through 2005. Then I found the average OWP for each age from 20-40. The graph of that is below.
It looks like the ages 21-28 are symetric with the next 8 years. So the overall OWP is the same in each period. If that happens for Pujols, then he will not change much. Without getting into the details, I calculated his OWP will be .768 over the next 8 years based on what he has done and what the historical trends are. I project that if he plays until 40, he will end up with about a .755 career OWP, staying 10th (Musial is 11th at .752). For what is probably a more scientific treatment of aging and performance in baseball, see PEAK ATHLETIC PERFORMANCE AND AGEING: EVIDENCE FROM BASEBALL by J.C. BRADBURY.
Below is the current top 10 in career OWP with 5000+ PAs
1 Babe Ruth .852
2 Ted Williams .832
3 Barry Bonds .810
4 Mickey Mantle .801
5 Lou Gehrig .797
6 Rogers Hornsby .787
7 Ty Cobb .781
8 Joe Jackson .780
9 Dan Brouthers .770
10 Albert Pujols .769
One last thing about Pujols. His career really does not have the kind of rising arc that the historical trend shows. So we can't be sure how any of this applies to him. Here is the chart of his OWP by age:
If we take his .827 at age 28 and then project each year forward using the changes in the typical trend, he would get .830 at age 29, then starting at age 30 and going on through age 40, he would get
0.820
0.820
0.824
0.791
0.791
0.787
0.783
0.755
0.749
0.748
0.712
Roughly he will have an OWP of .784 over the the rest of his career.
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