When I tried high mileage oil in my car, the performance took a hit and I returned to conventional oil. High mileage oils tend to have a stouter additive package as well as being on the heavy side of the viscosity range for whatever spec it is meeting. You can try it for yourself and see what you think, but I wouldn't bother unless the engine is showing some signs of age. That's just my opinion for what it's worth.
I bought some HM oil for my 93 Aerostar. As of yet I haven't used it, I might mix it 50/50 during my next OCI, and see if I can lower the oil consumption a little more. I actually changed from 5W30 to 5W20 and reduced consumption , I thought it would go up, or stay the same. When chatting with a friend he sent me something from Shell oil company that helped explain why that might have happened. Since joining BITOG I like to experiment a little.
According to Shell's study: "Lower viscosity lubricants give thicker top oil ring films", according to a chart in this study. Exact reason why I don't know, perhaps someone else who understands this better can chime in. This I believe can actually reduce oil consumption in some cases, if the consumption is caused by the rings. Guides are another story I would think.
JMO based on what I've read and am in the process of digesting. They used 5W40 15W40 and 5W20 for the study.
HM oils tend to have a heavier base stock than the same grade oil from the same brand. The HTHS is much better. HM oils will usually have more antioxidants, more anti-wear adds than the regular oils.
It is believed, and from advertisements, that HM oils have more/better/special seal conditioners. I am not convinced of this. I talked with Mobil and Valvoline and could not get an absolute answer on the more seal conditioner question. Since all GP II, III, and IV oils have to have seal conditioners anyway, it MAY be that they are just making a point of the seal conditioners in advertising their HM oils.
The 100C cSt of most 30 grade regular oils is in the 9.8-10.5 range. The 100C cSt of most HM oils is in the 11.5-11.9 range. 30 grade goes from 9.3-12.49. That puts the HM ois above the mid range.
I know lots of folk that use Valvoline MaxLife synthetic 10W-30 and Mobil 1 10W-30 HM in new cars and trucks. Valvoline MaxLife blend 10W-40 is also an extremely popular oil for new and low mileage pickup trucks, and SUV's.