I did some tests a while ago with the charge bonus of units, and it seems that insane charge bonuses (like 80 for hobilars) just don't work. There was a little discussion at totalwar.com, and it appears that 9 is indeed the maximum. There are some mods which have units with higher charge (like french knights in KekvitIrae's or Sicilian knights in Re Berengario's), but I doubt if this particular feature will be implemented correct.
As for bonus vs cavalry, I guess it is just another combat bonus (just as charge bonus), so maybe there is a limit for this stat too.

I was not sure about the things I wrote above, so I just did some other tests:
test1: changed every combat stat for halbardiers to 12, did a custom battle vs. feudal sergeants, halbardiers killed about 30 and lost 0 before FS routed
test2: changed every combat stat for halbardiers to 16, did a custom battle vs. feudal sergeants, halbardiers killed about 40 and lost 0 before FS routed
test3: changed every combat stat for halbardiers to 16, changed every combat stat for FS to 9, did a custom battle between the two. Halbardiers killed about 70 and lost 1 before FS routed
(I also changed morale to 12/16/9, that's why the FS kept fighting in the last test)

So, it seems that the hand-to-hand combat stats can be higher than 9. What about the charge bonus?

test4: peasants (with morale 12, charge 40) vs. hobilars. At impact both units lost about the same number of men (8), after that hobilars were winning easily, peasants routed with about 30 men left, hobilars had 26 men present.

And what about the bonus vs. cavalry?

test5: peasants vs. lancers. Peasants had attack and defence bonus of 100 vs. cav. Peasants killed 21 and lost 0 before lancers routed. So the bouns vs. cavalry can exceed 9. (if this wasn't the case the peasants should have an attack of 7 and 5 defence vs. the lancers, while lancers have 5 attack and 7 defence, so this should give both units about the same number of casualties).

Conclusion: only the charge bonus can't exceed 9 (which is a bit of a shame, because the cavalry charge, even a frontal one, should be really devastating against any unit that doesn't hold a pike or spear)