Gabe is right that its 40 for archers. Its on the tutorial at haypi.com. Here is a link. Scroll all the way down.
http://www.haypi.com/troop.htmAlso, that does mean 40 total which could mean 10 of each resource.
Just to clarify how overload works, lets assume you have 1 cav. If you attack someone who has an equal number of all resources, you will get 25 of each resource (for a total of 100). Now, if the person you are attacking does not have an equal amount of all resources, then you will take the resources that are most plentiful until they reach the level of the other resources. Some examples:
All assuming you attack and win with 1 cav and the person being attacked has a cranny level of 0:
Example 1:
Warehouse of Person Attacked Has:
100 Wood
100 Stone
100 Iron
100 Crop
Your attack will result in taking:
25 Wood
25 Stone
25 Iron
25 Crop
Example 2:
Warehouse of Person Attacked Has:
120 Wood
100 Stone
100 Iron
100 Crop
Your attack will result in taking:
40 Wood
20 Stone
20 Iron
20 Crop
Notice that after the attack, all resources have an equal level at 80.
Example 3:
Warehouse of Person Attacked Has:
120 Wood
100 Stone
210 Iron
100 Crop
Your attack will result in taking:
05 Wood
00 Stone
95 Iron
00 Crop
Notice that after the attack, wood and iron are the same and stone and crop are untouched.
Example 4:
Warehouse of Person Attacked Has:
120 Wood
110 Stone
130 Iron
100 Crop
Your attack will result in taking:
30 Wood
20 Stone
40 Iron
10 Crop
Hopefully these examples help and clear everything up. If not, let me know and I can try to explain further.