Determined by finding the last decade win% for every P5 team (including the 4 new ones) against 3 different types of P5 opponents; those with 3 or fewer P5 wins, those with 4-6 P5 wins, and those with 7+ P5 wins. And then taking sum of squares of differences to see which is most/least similar.
Most similar
1. UCLA
2. Northwestern
3. West Virginia
4. Texas
5. TCU
6. Washington
7. Washington St
8. Iowa
9. Baylor
10. Louisville
11. Arizona St
12. Penn St
13. Texas A&M
14. Nebraska
15. Cincinnati* (small sample size caveat)
Least similar
1. Kansas
2. Houston* (small sample size caveat)
3. Alabama
4. Clemson
5. Illinois
6. Ohio St
7. UCF* (small sample size caveat)
8. Oklahoma
9. Rutgers
10. Vanderbilt
11. Purdue
12. Colorado
13. Syracuse
14. Maryland
15. Oregon St
Have the data and spreadsheet now that I can make similar lists for any other school as well