Losi_b,
For the most part, it's trial and error to determin the best delta peak voltage value to use in the competitive RC vehicle world... This is because all we care about is how fast we can go on the track and little else...
Battery manufacturers (as oposed to battery matchers/re-sellers) probaby have some method for choosing what's best in their minds, and it may even be scientific. However RC racers rarely listen to them, since their goals and ours are rarely the same. Manufacturers are most likely interested in saftey, product life, and things like high output high current max proformance are probably kinda low on their priority list...
Hence... RC racers and RC battery matchers just play around untiull they get what they are after... max proformance.