Think you will find that the sleeve will give you a more consistent and larger bedding area for a large cartidge such as the RUM. 700 action is not noted for being stiff either and the sleeve will certainly stiffen it up.
However having said that. By the time you figure up the cost of a 700 action($300-350, truing($75-100), lapping lugs($25-40), sleeving$250-300), Hart/Sinclir bolt release ($60-80), etc, you can buy a custom action that will have twice the resale and cost less money than what you are proposing.
Go for the custom action.
BH