Ask Bradley... He told me he likes the spring 1.5 or so psi higher than what what he is tuning for. If he is tuning it, let him do the math...
Besides... There are only a couple spring rates that work if you go with the tial setup... 15.95 and 17.40... Unless you go with a different wastegate... Otherwise you need to put a MBC on the signal line like I did to dial it in better using the 15.95 setup...
But Bradley can look at the logs and tell which spring will work with the tune he is putting on it...there are more factors than just boost... Fuel pressure, wastegate duty cycle, and others...