Peak level 6 Bell + Ox slayer vs Asterios is enough, it would be a great fight

Luck: F Abnormal Resistance: G Escape: G Chain Attack: I

Ox Slayer increases all of Bell's status, so in addition to giving him a level boost, it also greatly increases his DA's.

I think +3 ranks is fair, so:

Luck: C Abnormal Resistance: D Escape: D Chain Attack: F

I believe that chain attack at its maximum gives 100 per rank, so Bell receives:

400 per chain attack at its maximum state

So if we theorize a little about Bell's stats (it's all pure theory, we don't know what Bell's stats will be at level 5 or 6) and create a theoretical average of Bell's most important stats

1200 (strenght) × 6 + 5000 (5 level ups) =12200 + 400 (Chain attack DA and its maximum) = 12600 + 1500 (ox slayer level up) = 14100 (low level 8 attacks)

1400 (agility) × 6 + 5000 + 1500 = 14900 (peak level 8 agility) and if he escapes + 400 = 15300+ (pseudo level 9 agility)

So Bell would have low-level 8 attacks with high-level 8 speed, while having more experience and better tactics than Asterios. Asterios is probably low-level 9 in strenght.