I'm about to do an oil change on my LS1 soon as well- the first oil change with me as the owner.
The previous owner tells me he used Castrol 10W60 full synthetic its whole life, and no engine issues. However I did find the car in a small private car yard, and I know they did an oil change. Nobody knows what they put in it, but it hasn't used any oil or given any dramas.
Based on my research, I'm going to try the Nulon 10W40 synthetic, in a 6 litre jug pack, as I've heard they like a little more oil in the sump. The Nulon also comes with moly blended in, and I am a fan of moly, having run it in all my other cars (when a rock hit the sump of my BMW M5 V8, the engine lost most of its oil and still limped on to a servo, was repaired, and the engine lasted another four years with no dramas- I had added moly to it)
I use Penrite mineral in the Centura 265 and am happy with it. And Penrite mineral in the RX-7 and it has been daily driven for near five years now with zero engine issues.
I'd just like to give the Australian manufacturers a go, and support keeping the dollars here in Aus. Penrite is good, so I just wanted to give Nulon a go in the Caprice LS1 and see what they're like.
I reckon go Penrite or Nulon, and keep Aussies employed, and keep us making our own good oils. Don't send your hard earned overseas to the USA or China. We're perfectly capable of making oil here in Australia that is as good as anything you can find anywhere else in the world. That's my take on oils