XP Gain

XP Gain is a great attribute that can help players advance faster in levels.
At level 150, a player can gain more than 30% of his level a day without having to use a single stam, just by XP Gain.

Every player starts out with +2 XP Gain.

There are items that can increase that XP Gain

• Shield of Bakmar (craftable, can increase up to +5 depending on craft)
• Fire Dragon Ring (+1 XP Gain)
• Jara Rune (+1 XP Gain)
• Writhing Ward (+1 XP Gain)

Set bonus can also include XP Gain

• Maximus Set (+1 XP Gain)
• Gurgriss Set (+1 XP Gain)

Relics can also give XP Gain bonus

• Despair Crystal (+200 XP Gain)
• Ethereal Pillars (+200 XP Gain)
  
• Krul Pyramid (+200 XP Gain)
• Searing Orb (+100 XP Gain)
  
• Unholy Shring (+200 XP Gain)

Finally, a player can apply an upgrade on his character for "+25 XP Gain (per hour)".
Each upgrade cost 15 fsps, and a player can apply up to 50 upgrades.
At 50 upgrades, that will add +1250 XP Gain.

On the character upgrade page, XP Gain is defined as such ::

Note that your 'xp gain' is allocated, plus a bonus of your xp gain times a multiplier equal to your level minus 50 divided by '25' (rounding down).
Note the actual value is always reflected in the quick display at the top bar xp mouseover. Note also at lower levels this value is then scaled down up to a reduction factor of 10 to stop it potientially being too overpowering. Below level 25, no additional bonus is applied.

That description is not concrete and wrong. As described above, the XP Gains are added up. A multiplier is then applied, and the multiplier is actually [Player Level]/25 + 1 (rounded down).
Note that there are no subtraction of 50 level as described on that page.
Also, the description of a reduction factor is vague. I will appreciate if any players below level 150 reading this page can let me know the values they observed.

I wrote a calculator to compute the XP Gain, and the value has been observed to be correct for level 150 and higher. The calculator can be found on the URL below :

http://sisland83.bravehost.com/xpgain.html


So above describes XP Gain, but what's the value of such attribute?
Many players will agree with me that Stamina Gain is probably the most important upgrade.
And XP Gain will come in a strong second. When that upgrade is maximized, it contributes about 10% of a level for level 400 players (and more for lower level players).
The 750 fsps needed to maximize the upgrade could have been spent to buy stamina for levels, but that will only get you about 10 levels (at around level 400). So you get to break even in 100 days. That sounds like a reasonably fair tradeoff. However, its value can be higher, especially if you plan and rest to recover on difficult levels (levels that will require a higher level CA to 1-hit).
But how does it compare to Stamina Gain, is it even better than Stamina Gain? For a level 400 player, each upgrade earns 425 XP per hour, while a creature kill gets you about 2200 XP per hour. So it is clear that Stamina Gain is much more valuable to a level 400 player. I believe that comparison holds true for lower levels also.

What about relics? Is it worth more than Stamina Gain relics? Those relics that provide +200 XP Gain effectively gives 8 upgrades worth in XP Gains, worth 120 fsps in value, compared to Stamina Gains upgrades that are worth 25 fsps per upgrade. However, that is the wrong way to compare. Instead, for a level 400 player, +200 XP Gain with the multiplier actually earns you 3400 XP per hour. While a single stamina earns you a single creature kill, worth about 2200 XP. Of course, the Despair Crystals has both +200 XP Gain and +1 Stamina Gain, making it the most desirable relic. OK, so it is moredesirable than a Stamina Gain relic. But is it really worth all the walking? Assuming one needs about 120 stamina to return to the relic and back to the hunting grounds. That is 264k XP. To break even on the XP gained, one has to stay on the relic for 3.24 days. That clearly is valuable to some players with enough maximum stamina. But what if not all the players need to return? Let's say, only half needs to return (with players taking turns perhaps). Then it should be clear that the relic is very well worth defending.

What about items with XP Gains? The Shield of Bakmar adds +5 XP Gain. But at level 400, that adds 85 XP per hour. Those +1 XP Gain items add only 17 XP per hour. But that XP is much less than a single creature kill. In fact, the Shield of Bakmar only add 2040 XP per day, and a single Stamina earns you more than that. It is still all nice, better than nothing at all. However, if you have to spend 120 stamina to walk back to a relic, you really should be willing to give that up. Assume 9 players with 9 slots for defense. If you use the shield, there's really only 8 slots for defense. Instead, if only 8 players return (the 9 players can take turn on who can stay out), and not use the shield, they can get the same total defense, and save 120 stamina. Compared to all 9 players returning and getting 1 stamina worth in XP every day, it'll take 13 days to break even against the 120 stamina.