I've noticed that for example both M1 and Pennzoil both advertise their cleaning ability of their oils but in the fine print they both say they use only 5w30 for the test. Is there a difference between the 5w30 and 5W-20 or other grades in regards to the cleaning ability? Reason I ask is that when looking at the product data sheets, it seems like most oil manufacturers have 5w30 as their "best" grade going off purely spec sheet numbers. Noticed this for Valvoline and Quaker State too....not just M1 and Pennzoil.