Reading this thread has been interesting. The Emissions on the Gen 1 Diesels, and Diesels in general have been a technical challenge (though it seems the made big improvements on Gen 2 - 1.6L over the Gen 1 - 2.0 for emissions).. it appears that a similar challenge is now taking place on the engine pistons in the gas engine... All this due to CAFE standards, and EPA standards.. Having said that, if I was driving a gas engine, I'd go high octane for sure, I've calculated that even in my 21 year old Saturn, that the MPG increase for the more efficient burn of the higher octane fuel more than offsets the extra cost of the fuel, I'd assume that holds true, even more so for a turbo charged engine in the Cruze.
The other observation.. I think I'll take the possible emissions hassles over a blown piston... then again, I have 3 Diesel Cruzes, so that should be pretty obvious I guess. Actually the diesel emissions tend to work pretty well if you do enough highway driving to get a good DPF regen, I've been without any serious issue on my Diesels because I have a pretty good understanding of what it takes for them to work well.
It's also interesting to hear about soot issues on the gas engine.. that's been an issue for Diesel, especially from EGR flow, which tends to be much higher in the Diesel.
To the OP: Do consider a diesel for your next 50/50 highway/city car... my car with average speed at only 25MPH is sitting at 50MPG right now, I've been stunned at how good the MPG is on the Gen 2 Diesel.
I'd caution against a Diesel for anyone doing mostly city/short duration drives.. that spells emissions troubles for sure. It would really be nice if the manufactures would just explain all that, but they want us to think any and all cars can do any and all patterns of driving with no problems... which is just not reality. I do think they say 87 Octane is OK, for marketing purposes, when clearly a turbo engine with higher compression is going to be safer and perform much better with the higher octane fuel.... this is the marketing people, likely over objections of the engineers.