One of the nice things about Mobil 1 Tri-Synthetic 5W-30 (dunno about the new SuperSyn) is that it doesn't use any VI to achieve the 5W-30, at least from what I've read.
So, I doubt the viscosity spread in that case is much of a concern. When considering an oil with VI, you want to choose the lowest spread possible to minimize the VI in there, as has been noted.
For Derek D., I say use the Mobil 1 5W-30. It's what I put in mom's 01 ZX3 (screw that 5W-20 stuff). However, if you ask 10 people around here, you are probably going to get 10 different answers, so don't expect anything definitive. Just like if you were to ask what car polish/wax to use ... :rolleyes:
