This is only my third post but I think this is something I can comment on since I work for an auto manufacturer and am an ASE Certified Master Auto Tech. There is no way I would leave the factory fill in for more than 1,000 miles unless it was a leased vehicle. If it was something I wanted to keep a long time I would actually change the oil and filter at some point between 50-500 miles. The majority of "break-in" and break-in wear occurs within the first 50 miles. By the time the vehicle has travelled those 50 miles, the engine has made aproximately 200,000 revolutions (on average). By 500 miles, its made well over 1,000,000 revolutions and likely gone through several heat cycles.
My personal preference would be to change the oil at 500 miles to a full-synthetic, although you could certainly use a convential from 500 miles to whenever your next interval, your personal decision. I've had the chance to "break-in" two new engines in the past few years, one was a leased GMC truck, one a new Harley. I changed the leased truck oil at 7,500 per the owner's manual (with the cheapest oil and an AC filter each time) and every 7,500 miles thereafter. The truck never used more than 1/4 qt. between oil changes or had any mechanical problems during the 36 months/20,000 miles I had it. The Harley's oil was changed at 453 miles to full synthetic. This is the third season with the HD and it used about 4 oz. of oil this year, during stop and go traffic in Sturgis (90-100F) so far (4,000 miles) and, also has no mechanical problems. I also have a 2004 Grand Prix that I got with 8,000 miles on it. The original driver changed the oil once at around 5-6000 miles (when the OLM went off). I now use full-synthetic and use 0 oil between OCI's of 8,000 miles.
The only Cadillacs that I know of that use synthetic as factory fill are the "V" series and the XLR. The Cadillacs that had consumption problems in the past did NOT come with synthetic. I am unaware of a consumption problem with Corvette motors beyond the normal consumption if/when the vehicles are raced. I owned a 1994 Cadillac STS which was one of the common models known for consumption (4.6L Northstar) and I used synthetic oil consistently. I sold the car with 152,000 miles and it used about one quart between oil changes (10% oil life left, approx. 5K miles). Usually, it was about time to change the oil when it was one quart low. The person I sold it to used synthetic for 1 or 2 changes and then switched to conventional. After the first oil change to conventional he said he was using 1qt in less than 1,000 miles.
Long story short, several vehicles now come with synthetic from the factory and sometimes even the same engine is spec'd for synthetic for one model line/option level and for conventional for other lines/models. I doubt that the engines are manufactured or spec'd out any differently. Manufacturers know that certain customers are willing to pay for synthetic and other aren't. Perfect example: Corvettes and the late Trans Ams/Camaro Z28s. Same engine, different oil. Also, the CVO Harleys come with synthetic while the others don't. Same lower end, same machining of the cylinder walls, etc.
Determine how long you are keeping the vehicle. If it's beyond the BTB warranty, then at least change the oil (well) before 7500km.
