As you balance your acid and your potassium sorbate, the research by Schnaffer shows that you generally have more success with a lower pH than you do with additional Sorbate. Since your beverage is sweetened my recommendation would be try to get it all the way down to 3.0, that really prevents a ton of growth and improves the performance of your potassium sorbate (by keeping more of it in solution as sorbic acid).
Your potassium sorbate acts as a weak base, so be cautious that the more of it you use the more acid you will need etc. etc., start by getting your target pH or lower then add whatever amount of PS you want to test.
When it comes to mold growth, accelerated testing is next to useless as mold just doesn't grow faster by incubation etc. really. And a 0.1% failure rate won't be visible in most sample sizes, but will definitely be visible to your customers every 1/1000 bottles.
Mold spoilage modeling:
bacteria modeling (less relevant if you're pasteurizing)