FWIW, back in the 80s I worked in a buick dealership, and had access to see the GM tech bulletins. GM has recommended against using any brand of 10W-40 oil because of the additives problem with gumming up rings on the pistons. I quit using it then, and have continued to only us 10W-30 in my own, and customer vehicles.
I personally use mostly Pennzoil, and have had zero trouble in the last 40 plus years with their oils. On occasion I have used some Walmart full synthetic (Super Tech), but always stick with the 10W-30 weights in my cars, winter, or summer.
Pontiac originally recommended 5W-30 in the GTO LS engines, but later changed it to 10W-30, which is what I started using from the initial oil change when I bought it new.
From my experience, you'll be fine with 10W-30, and keeping oil clean is much more important than what weight, and brand, is in the engine.
