PLEASE bear in mind that every car is different, but these are the settings I used when I ran more modest boost (on a GT28R)
Channel 1 - 0.8 bar, gain = 10 (nice and gentle, great for fuel consumption)
Channel 2 - 1.0 bar, gain = 12 (still gentle, but allowed me to beat almost anything else on the road)
Channel 3 - 1.3 bar, gain = 20 ("point & squirt" mode - lots of boost, coming in very quickly - max torque)
Channel 4 - 1.4 bar, gain = 10 (Max boost for max power, but gain reduced to prevent spiking)
A smaller turbo would need even lower gain settings - maybe even into single figures
Don't forget to set the boost limit - great safety aid - I often get spikes into 1.8 bar on my current setup - without the limiter, I'd probably exceed 2 bar