Chances to get Merciless + King's prefixes are really slim. 1:300 (from an old calculator / memory)
That means it takes an average 300 imbues, or 12.5 full accounts of leveled chars. However if you have imbued 100 times already, that doesn't mean you chances are increasing.... deg. gamblers often believe it does, which is known as the gambler's fallacy.
If you set on a journey to create 300 imbues, there is still a chance of 36.7% = (299/300)
that you won't get those 2 high ED prefixes.
For 8 chars --> 24 imbues there is a cumulative chance of 7.7% that you get something high dmg (Merciless+King's).
At clevel 74 you can get all the best stats except +20 str.
Imbue Mart at character lvl 74 --> thus creating a ilvl 78 Martel.
/end of guide