Well, you can reach that when you cast death sentence and sudden strike on a person, then use recharged arrows and a slow bow.
The discussion about marks are overpowerd is just now because many marksmen build up their skills in this way lately. But when you build up your skills like this you are not overpowered in other combat situations. He lacks either on protection/evasion spells or on other damage spells, that means the marks need to relay on these spells.
When you don't switch from fast to slow bow in mid combat you cast death sentence, then you need 3,5sec, then you cast sudden strike, wait 3,5 sec, cast serpent bite, wait 3,5 sec and cast lethal strike(with a 34% chance of high dmg) [not to forget to have recharged arrows activated]. But when you switch weapon...then you are really deadly...
As I said marks have to relay on this spells to kill someone, like a real sniper. And that is what marks are.
In my humble opinion marks are not overpowerd, they are just balanced. But as you can see I say that just because I am a marks, so I don't want to loose power...and I cannot really realize how strong marks really are since I am one.
And yes, I agree with wudy, that the rp ranking is a indicator of success, and of power of a class. I guess that is why barbs will loose some powers. Actually barbs have much rp because they deal much dmg, and when an enemy has only 100 dmg left because others hit him, and the barb hits it then for 1000dmg, then the barb gets rp as if he had dealed 1000dmg and not 100, but that is another issue.
Edit: Yes, Vengala is well know as someone who's lethal strike does almost always highest damage, and who hits you 5 times when you attack once...I still test how he does it...and when I found out all elves will die...muhaha