I am currently using the graphire2 4x5 tablet and am looking to upgrade to the intous3 fairly soon. Would buying a bigger tablet be beneficial to retouching at all? It seem like my arm would just get more of a workout

The cost between the two doesn't matter. (I wish I could justify the cost of the cintiq tho!)
Right now my reasoning is to buy the 6x8 even though I know that I might be turning it down closer to the 4x6 area...would be good to know that I have the extra room if I need it, however if I know I wont be using it then its a waste of $75 and deskspace
Any input would be greatly appreciated!