I'm not sure it really matters much, if the guy you are starting is likely to be yanked early. I guess one could argue a true pen game is when the starter will be yanked early, even if he is doing well.
Here is our W-L records with our non top 5 starters (I guess we did worse than I thought):
GS Pitcher team records (pitcher ERA as a starter)
8 Velazquez 5-3 6.75 (22 IP)
7 Johnson 3-4 5.09 (23 IP)
6 Cashner 1-5 8.01 (30.1)
5 Chacin 2-3 7.90 (13.2)
3 Weber 2-1 7.94 (11.1)
3 Lakins 0-3 0.00 (5.2)
2 J Smith 0-2 9.82 (7.1)
1 J Taylor 0-1 0.00 (1.0)
1 D Hern 0-1 9.00 (3 IP)
1 Poyner 0-1 0.00 (2 IP)
The bottom 5 were the obvious "BP games" and we went 0-8 in those starts, despiye some good efforst by some of the "starters".
Interesting to note that the two guys we brought in from outside the organization went 3-8 with an ERA just under 8.00.
The team went 8-7 in Velazquez and Johnson starts combined. (10-8 adding Weber)
Note: we were 7-5 in Eovaldi's 12 starts. We were 18-14 in Porcello's starts.
25-19 Eovaldi+ Porcello .568
10-8 Johnson, Velazquez & Weber) .556
Basically, a 1% better chance of winning with our #4 & #5 slot starters over our #6-8's.