Thanks for all the good input!
The car has 105,000 on it now, and since its the most quiet Cavalier I've heard start up, I'd like to keep it that way.
By the sounds of it, my initial plan to keep it on 5W-30 is in line with the long term results posted here.
I would like to move it to something better than basic dino after a bit, but I don't want to upset the groove its in.
I've used commercial oils for awhile, especially after hearing about the change in anti-wear components in consumer oils (a year and a half ago, was it?). There isn't much in a suitable weight for this car in Rotella locally, though.
I've recently tried synthetics, trying to make another high mile vehicle last longer, but with mixed results - possibly related to the weight oil I initially tried. So, I'm trying to learn from that, since most of my experience was with older engines.
From what I've heard over the years, Mobil 1 seemed at its best when used in engines that are nearly new, or at least very clean.
Locally, a synthetic blend was suggested as a transition oil to full synthetic, following some cleanup changes.
All things taken together, I think I'd rather move no further than a good synthetic blend, if I knew of one that would hold up well, like Valvoline Durablend did when it was first introduced.
Thanks again for all the good info so far!