These cars do use quite a lot of oil when run hard. Assuming you're referring to the pressure drop when you're driving, not the level on the dipstick? By switching to a 0w/40 you will see even more of a drop. Unless you are in very cold region you don't need to go to such a low visc oil. Consult your Owner's handbook. It has a very clearly marked page identifying what oils to run in our cars. It is still relevant today. In Sydney where it is warmer than where you are, we run 20w/50 on the road and 25w/60 on the racetrack.
Also if you are hell bent on using Mobil 1 which seems very popular in Northern America on the basis of what Porsche US and dealers all use, make sure you find one that has sufficient levels of ZDDP in it. Note, there are numerous oil threads on all forums. The most comprehensive is the Pelican one. Enjoy. ;-)
http://forums.pelicanparts.com/porsche-911-technical-forum/367300-ultimate-motor-oil-thread-why-we-hate-cj4-sm-oils.html