I use premium but when you think about it, the 2.4 turbo on regular fuel with SN GF-5 oil (not SN-Plus, not Dexos 1 Gen 2) seemed to have no problem. These older oils were more prone to react with fuel in a way that reduced octane. Using SP/GF-6 gives added protection against that. When I first got the car I was afraid of LSPI but it's been 2 years since it's been used in the Ascent and I do monitor their forum and I'm not seeing any issues.One thing that concerns me about using 87 octane is the PCV system. I have a UPR dual stage catch can on my F150 Ecoboost and I get quite a bit of liquid out of it in the Winter. It's mostly water condensate mixed with oil. Just small amounts of oil in the Summer. I have no doubt this sludge mixture coming through the intake valves would reduce the effective octane of the fuel.
If you're using SP/GF-6 then the potential harm of reduced octane from oil is decreased. I use premium mainly for the increased detergency for the direct injection fuel injectors in Shell V-Power.