Well, I've never made a script for this before but I'll give it a try. Just, for future help with lua, I think you'll find every page in this section VERY useful: http://www.arcemu.info/wiki/index.php?title=Lua
Anyways, I IMAGINE it would be something like this:
Code:
function PvP_OnKill(event, pPlayer, pKilled)
local level = pPlayer:GetLevel()
local deadlevel = pKilled:GetLevel()
if (level <= 40) then
pPlayer:GiveHonor(level*deadlevel)
pPlayer:SendBroadcastMessage("Some honor for yous")
end
if (level >= 41) then
pPlayer:GiveHonor(level*deadlevel*2)
pPlayer:SendBroadcastMessage("More honor for yous")
end
end
RegisterServerHook(2, "PvP_OnKill")
Pretty much all this does(if it works!) is check the player's level when they kill someone, and then multiply that number by their dead opponent's level. If they are OVER level 40, then the result is doubled. The reason I didn't use 23(ON_HONORABLE_KILL) as my server hook is because I thought you may want players to be given honor even if they pwn a level 1.
If you only want it to modify the honor given on honorable kills.. well, change the 2 to 23 I guess. And uhh, you can remove the broadcast message if you want. I just like stuff like that. 
I can't be sure about it working or not, because currently my server isn't public, so it's just me on there.. it's pretty lonely. xD
If it works, you can play around with it to your liking. But really, read the wiki. It's amazingly helpful.
If it doesn't work, oh well. I tried. :/