Fast68 : yea, thats the main problem with oil these days. The oil becoming saturated with carbon. 8-10K seems to be the sweet spot.
One major benefit with synthetic is its harder to burn it which is a big benefit if running a turbo. I have a feeling it helps with the iron heads on the 3.8's which most likely cook the oil a little more then aluminum heads, however that is just an assumption on my part.