If I remember correctly it's a 15% combat bonus on hard and 30% (about 1 valour) on expert and plus 4 morale (on expert) in MTW. I think it was someone from CA who said those numbers.

I'm guessing that the higher killing speeds with the combat bonuses makes things alot worse in RTW, considering that in MTW you aren't recommended to put two equal units to fight on equal conditions, but had higher ground or flanked them, but in RTW you don't have enough time to react.

The bonus don't need to be bigger in RTW.

This is only a guess based on opinions from the forum, considering that I don't own RTW.