Wow-- thanks for the update. Unfortunately not good news. But important. 
Yes, not good, but important.
Although this study wasn't able to establish a 95% positive predictive value, it did mention an older study -
Lastly, Ho et al. identified a sesame SPT wheal diameter ≥ 8 mm as being predictive of a positive food challenge with > 95% accuracy.
Ho MH, Heine RG, Wong W, Hill DJ. Diagnostic accuracy of skin prick testing in children with tree nut allergy. J Allergy Clin Immunol. 2006;117(6):1506–8.[PubMed]