Tabetha, not having a go, or trying to be argumentative, but i have seen evidence of the siemens being superior to greys in regards to idle.

Both were 4x4 sapphs on l8's.

Car one, MSD chip, Greys etc etc - Shite idle until the closed loop was plumbed in.
Car two, MSD chip, Siemens etc etc - Perfect idle even without the closed loop connected.

Thats my experience with them, just thought i'd post that up