i work on industrial engines offshore for a living. everymonth we send in oil samples for all the equipment that i work on offshore. the oils we use were rotella t and mysella 40 low ash and now pegusas 805. (all from shell.) the samples are sent in to tell us when we need to change the oil. (money saving thing so we dont waste oil by changing to much.) with the mysella and pegasus we change oil and filter every 3000 hours which pretty much adds up to 3 months. with the rotella i changed the oil annually. they would suggest changing the filters but thats it. this is on engines that displace 9390 cubic inches that compress 10 million cubic feet of gas everyday and run 24 hours a day. all they do is work under extreme loads. now i am sorry but after seeing that with my own eyes i will run rotella in everything that i own. the only oil that i have even seen to impress me more than that is royal purple. they have this display thing that grinds 2 pieces of metal together. with regular oil the metal would smoke and grind away. they put one drop of purple mixed with the other and put it on the grinder and it wouldnt even smoke. i am sure you can find it on youtube. anyway i just thought i give my own opinion and experience on the subject.