A general guidline: Here

After looking that over there's a few simple rules that should be followed:
  1. The math, a short breakdown:
    • If you are getting 1000 exp per kill with an avg. kill speed of 1min this is 1k/min == 60k/hr
    • If you are getting 500 exp per kill with an avg. kill speed of 30 sec this is 1k/min == 60k/hr
    • If you are getting 250 exp per kill with an avg. kill speed of 15 sec this is 1k/min == 60k/hr
  2. Experience chaining, a short breakdown:
    • First kill: no bonus, no timer
    • Second kill: 20% bonus, 100 seconds
    • Third kill: 25% bonus, 80 seconds
    • Fourth kill: 30% bonus, 60 seconds
    • Fifth kill: 40% bonus, 20 seconds
    • Sixth kill and beyond: 50% bonus, 10 seconds
  3. Mob linking, a short breakdown:
    • One linked mob: 25%[\li]
    • Two linked mobs: 50%[\li]
    • Three linked mobs: 75%[\li]
    • Four or more linked mobs: 100%[\li]

From this info we can safely say that a few things are undeniably true.
  1. If your party can manage to kill 8 mobs per minute even though they're worth only 200 exp per kill the exp per hour will be significantly higher than if your party is killing 1 mob per minute worth 1000 xp. 1600*60 > 1000*60, it's not a small amount.
  2. Experience chains that last only 1 or 2 kills because your party isn't able to kill mobs fast enough to maintain a chain your bonus experience will suffer. 1000 xp per mob rotating from chain 0 to chain 3 will give at that same 1 min. per kill, 1000 + 1200 + 1250 + 1300 = 4750 every 4 mins * 15 == 71250 exp per hour.
  3. Experience chains from lower leveled mobs where your avg. kill speed is 8 mobs per minute = 7.5 secs per mob so with a base exp per mob of 200 you end up with, 200 + 240 + 250 + 260 + 280 + 300 + 300 + 300 == 2130 per minute == 8520 per 4 mins == 127800 per hour.a difference of over 55000 per hour that's about 1/2 level per hour from 45~50, nearly full levels below 40.
  4. If you then manage to regularly achieve a link of 4+ mobs, typically a very dangerous prospect when fighting mobs that are worth 500+ base exp, you will effectively double these numbers, meaning that in 1 hour you can gain 140k on higher leveled mobs if you can survive, or more than 250k per hour on lower leveled mobs that your party has very little to worry about from even if you pull 2~3 groups at once unintentionally.

From the above examples, while they may seem a bit in the extreme the facts are the same no matter how you break down the numbers.
Using this logic to develop an approach to where to level and what to level on would lead to a few simple rules worth following:
  1. Keep party level as close to one another as possible, aiming for no more than 5 levels difference between the highest and lowest members. This should ensure that everyone is able to serve a purpose and keep things moving smoothly.
  2. Find mobs that have a level range that is at least 3 levels but not more than 8 levels higher than your highest member, the larger the gap between members the more important this becomes, a level 40 as your highest fighting level 45 mobs should go well, but if the majority of the party is 7 levels lower, well 33s fighting 45s isn't a great match.
  3. If it's at all possible find mobs that travel in large groups but don't aggro, this will make it significantly easier to get links while not getting unwanted adds.