I would think 75/25, dino/PAO would be cost effective and still provide the benefits of PAO. You could increase or decrease the PAO content, but cost and performance will shift accordingly. For PAO, I would choose M1 and Pennzoil for dino.
Not true! That's what we've been lead to believe. All oils are 100% compatible with each other. All oil blenders approve of mixing brands in case of emergency......they don't want you to use the other brands because they will lose your business. Mixing synthetic and dino will shorten the synthetic's life expectancy, but extend the dino's life.
Since I know most of us here (99.0%) do not go beyond 5-6k miles, the mix should work well for cheap.