Here are some rough "first order calcs":
The average ERA by rotation spot is:
1: 3.60
2: 4.14
3: 4.58
4: 5.10
5: 6.24
(Source:
http://www.hardballtimes.com/main/ar...ur-4-starter/)
For the sake of argument, to calculate win percentages let's bump those up by 4% for unearned runs. Using the league average runs scored of about 4.85 (2006 full season average) I get win percentages (Pythagorean) of:
1: 63%
2: 56%
3: 51%
4: 45%
5: 36%
Those calcs assume that the starters pitch the whole game though, so the actual %s are probably "flatter" since each pitcher gets (on average) equal support from bullpens.