The Mk6 start does seem like the best solution so far. However it's most certainly not 100% WR. The best we can say is some very close to 100% winning the ult race. However there is a risk of timing out even putting on auto as soon as ult is reached. I've been winning most of the battles [Edit: the "small sample size" disclaimer] so far but the timer can come down to anywhere within 30 seconds. My personal record I believe is 0:05. Granted it will get better as I muscle memorize the sequence, bad rng can still lead to losses.
Another caveat is that if the opponent brings out Mk6 as the 2nd RI, and one shots your dagger, things can fall apart real quickly. BitDynasty released a solution to that, but even then he admited that "1 out of 4 times" it wouldn't work due to bad rng.