Some people mistakenly think that 0-40 is thinner than 5-30 which is clearly false. This oil is extremely good for low temperatures, but it isn't just that. Its vital role is played during the first minutes of engine working as at this point it is better than other oils. Before that i have been using Motul 8100 10W40. I clearly saw difference in revving high with mobil 1.
Still i don't keep this oil for more than 6000km, or less if i enter track or perform spirited driving. After aprox. 5000km i have seen some oil consumption but it is minimal. From 100-300gr most.
Have a look here
http://www.v8sho.com/SHO/Mobil10W40.htm
It holds its features and outperforms most competitive oils
* Kinematic, cSt @ 40°C 80.3 (0W-40) vs. 53.7 (5W-30)
* Kinematic, cSt @ 100°C 14.4 (0W-40) vs. 9.7 (5W-30)
http://www.mobil-1.co.uk/cms/Home.aspx