45% tallow with 25% lard makes a really nice bar. Adding in whatever else you want for oils. Vinegar or any acid for that matter, neutralizes lye, which is why it ups the superfat. What are you trying to accomplish with the vinegar? It will not lower ph but will make a harder bar of soap.
To use vinegar, take the amount of vinegar you want to use and mulitply that number by 0.03570, which will give you the amount of extra NaOH to add. For instance 85 g NaOH x 0.0357 =3 grams extra NaOH needed. This is easier than just trying to lower superfat to compensate