My understanding is the IMX174 is also Exmor R and BSI. Pregius is their designation for a global shutter. Global shutter takes a little extra real estate on chip, a few extra gates and control paths. This cuts QE a little bit and adds a little noise.
It's not, check Sony description of that sensor.
Thanks, Piotr. So the 290 is a BSI. That would explain why it is so sensitive.
For small pixels in CMOS sensors BSI rescues fill factor and allows the to work efficiently. IMX224 isn't BSI yet it's higly sensitivy with very little read noise. BSI on such sensor doesn't have the effect that BSI on large pixel CCD/CMOS has when designed for high end performance.