Is there a standard percent that the 'capitol' world operates above others?
You can click on the Civilization Capital tile and it'll list the bonuses.
Originally, it was Food +10, Industry +24, Research +24 and Influence +25%, but that might have changed in TA.
Will capturing another races 'capitol' world give the same vamped up percentages as your own 'capitol' world?
Yes and no. If you capture the enemy's capital, it'll just switch it to another planet. When it does that, you lose the capital bonuses. The initial planet view might show all of the bonuses and pop of a capital, but that'll change on the next turn. Any excess population that the Civilization Capital was feeding will also die off during that turn.
To keep the capital planet as such, you need to completely eliminate the enemy during the turn when you capture the capital. You can also manipulate this by taking enemy capitals until it chooses one that you like. (Capital planets appear bigger in the icon view to help you keep track.) Once done, destroy the enemy, taking the capital planet last and it'll be yours with all bonuses intact.
Minor race capitals also give the bonuses and are easy pickin's.