Okay, so I did the testing against MF-H Flash Orion W145MF, and I had to do 30 rounds because I got such incredibly odd results the first 20 rounds:
MF-H Basalt Horogium R145RF vs.
MF-H Flash Orion W145MF
Standard Procedure, BB-10, Beylauncher L/R with Suspension
Flash launched first on even launches, Basalt on odd
1. Flash KO
2. Flash KO
3. Flash KO
4. Basalt KO
5. Flash OS
6. Flash OS
7. Flash KO
8. Flash KO
9. Flash KO
10. Basalt KO
11. Basalt KO
12. Basalt KO
13. Basalt KO
14. Basalt KO
15. Tie; Basalt KO
16. Flash OS
17. Basalt KO
18. Basalt OS
19. Basalt KO
20. Flash OS
21. Flash OS
22. Basalt KO
23. Basalt KO
24. Flash OS
25. Basalt KO
26. Basalt KO
27. Flash OS
28. Flash OS
29. Basalt KO
30. Flash KO
Basalt Wins: 15 (14 KO, 1 OS)
Flash Wins: 15 (7 KO, 8 OS)
Basalt Win %: 50%
Yep, dead even. This was a very interesting battle, since the first ten rounds Flash dominated, but the second ten rounds Basalt took almost every win. If for some reason neither custom gets KOed, Flash almost always won thanks to its stamina (with only one exception). This is one of the closest non-mirror matchups I've ever seen, heh.
I alternated launches because I treated this like it was an Attack vs. Attack test. It never seemed to matter which was launched first when everything was said and done.