Well, let's say I have a Dwarf PC with 19str, carrying 340lbs of gear, which includes the adamantine platemail he is wearing.
First off:
Carrying capacity is determined by Strength. 19str is:
Light - 116 lb. or less
Medium - 117-233 lb.
Heavy - 234-350 lb.
So = 340 lbs of gear means the dwarf's encumbrance is immediately in the "Heavy" category.
Secondly,
Armor comes in Light, Medium, and Heavy versions. Each corresponds to an encumbrance category. Even if you are carrying nothing else your encumbrance can change depending on your worn armor type.
So = the adamantine platemail also places the dwarf in the "Heavy" encumbrance category.
However,
SRD said:
Dwarf base land speed is 20 feet. However, dwarves can move at this speed even when wearing medium or heavy armor or when carrying a medium or heavy load (unlike other creatures, whose speed is reduced in such situations).
As you can see from the quote above, Dwarfs suffer no speed penalty when under medium or heavy encumbrance (of either type).
So = a dwarf can move just quickly with 340lbs. of gear and full plate as he can carrying or wearing nothing. (though the Run option is impaired)
Lastly, - and here's where things get interesting.
SRD said:
Tumble - You can’t use this skill if your speed has been reduced by armor, excess equipment, or loot.
Ignoring whatever "loot" encumbrance is, this skill is plainly unusable by anyone with any kind encumbrance penalty - unless they happen to be a dwarf.
So = A dwarf with a total tumble skill bonus of +15 or better can tumble around his enemies, in adamantine fullplate, carrying 340lbs of gear, with relative impunity.
I wonder how many 10' poles he could purchase before reaching 340lbs.