IMHO and based on my own struggling with the GSH or GGH for my BG City, I realize that it's really not an easy choice. However, I have to say that based on my Turqoise color I have seen IRL, I would think that the GGH will stand out more. The GSH looks good as well and totally agree with Decophile's comments about warm/cold colors.
In general, the blue color should be the cold color family. However, as Turquoise should have a hue of green, I would say it goes a bit to the warm color family. Also because blue+yellow=green. Therefore, I would suggest the GGH to make the 08 Turquoise a bit closer to the true Turquoise (with a hue of green).