Finally, I got Stage 1 and tried!
0-60mph of my stock 328i without Stage 1 was 5.920sec.
(Roughly 5.8 - 5.9sec was average time.)
After Stage 1 installation, it was 5.452sec!!
(I tried several times. As average, it was around 5.5sec.)
Again, I didn't do any tuning without BMS JB Stage 1.
Default boost is still +3psi. (Not changed.)
I didn't use a launch control.
I got 0-60 time with Torque Pro app / OBD2 adapter.
Here is an evidence.
[u2b]
[/u2b]
I wanna try with +4psi at some future date ;-)