2.5-3 stacks imo. I bought mine for 3 but that had 20N. It is easy to say 5 stacks and play into the placebo hype of the item but when it comes time to actually pay the price, I think many people will find that pretty steep.
If an SJS drops, chances are it's going to have stats you don't want. This is an 0'd SJS we're talking about, likely to be sphere-able in any areas, great for making sets.
Getting an SJS is kind of like winning a lottery, while grinding PDs is much less so. I think this is one of the items that grinding PDs to sphere it is probably more feasible than waiting to get/buy another drop.