Due to its short shelf life it does get passed over in soap making quite a bit, and it doesn't really add to much to the bar. I would use no more than 15% I have found that I like 10% because then I can add that 5% somewhere else like coconut or palm for a harder bar. OR - swap out that 5% for castor oil. That is a great little addition to any soap recipe (adds to the bubbles)
Standard safflower ... I agree with what the others are saying.
High oleic safflower is closer to olive oil in its fatty acid makeup, although I wouldn't make a 100% HO safflower bar like people make castile. I do use it consistently for part of my liquid oils and like it very well.
Does the "use by date" on the oil not correlate to DOS? I'm just confused because I just bought a bottle of safflower oil today and the "use by date" is June 2015. That seems like a long shelf life to me! I can't tell on the bottle if it's high oleic or not. Where would one look? The ingredients just says "safflower oil."
If it's high oleic it will say so (or should). I have a bottle of high oleic safflower oil and it soaps nicely. I find that sunflower/safflower soaps make a gentle soap, excellent for the face or sensitive skin. The only downfall is that the bars are softer. Use additives to make it harder but keep the percentage to around 25% or less for non high oleic oils. Best to experiment, IMO.