160 is bad for the motors according to reports, engine temps can still spike frequently to about 220 or more, then dropping to 160 again. This happening repeatedly can cause mild or worse warpage in the cylinders and heads.
Best bet is probably a 180 with an upper end coolant like DEX-COOL (from GM dealer) or Texaco-Havalene from autoparts store, both of which are Ethylene Glycol based as opposed to Propylene Glycol. Eth. Glycol has higher heat tranfer ability, as well as higher quality additives for corrosion inhibiters than Prop. Glycol
*edited*
Here is what I was reading, from 60degreev6.com
http://60degreev6.com/modules.php?op=modlo...artid=16&page=1
Further, here is a previous discussion on the topic within this board, but I think the related articles had more to do with a 3800, but I'm sure the same principles apply:
http://invision.aleromod.com/index.p...ic=6372&hl=160