I may be wrong, but I don't think there's a single manufacturer that recommends a multi-visc oil that includes going up to 40w. The VI improvers needed to get an oil up to 40W have proven to carbon up on the rings and cause major problems.
Way2old may use it on his fleet, but you take his advice at your own risk. My advice, stick with 5w-20. It's more energy efficient and reduces start-up wear.