the bigger the setup, the larger the wastegate you want to go. the larger housing will allow more wasted air to leave faster and result in less chance of a boost spike.
a 38 is good for 350+ ~ish
i have a 40 on my setup
46 is for all out drag cars, and huge power supras, etc...
.XX bar is the spring, or the LOWEST boost setting you can run on it.
.5-.7 is average i'd say (about 7-10 psi)
generally, a boost controller is good for upping the boost double the amount of the spring. so if you plan to run 20 psi at the track, amek sure you are ready to run 10 on the street