The alleged implications of "additive clash" are overstated. (Whoever originally penned the notion that mixing conventional and synthetic oil would lead to congealing should be strung up by his thumbs and lowered into a vat of boiling used oil just changed at 25,000 miles!) The allged "additive clash" implications are also further minimized by staying within brand. Given that many, if not most, commercial blends are no more than 10% Group III or IV, going with a 1 + 4 mix still makes for a 20% proportion of syn, and cheaper than the commercial blend to boot. Since all the major oil companies unequivocably state that it's OK to switch from conventional oil to synthetic oil (and back again, if desired) <i>without</i> running a flush, and since at least a 1/2 quart of whatever was run previously remains after an oil change, this really isn't rocket science, guys.