[brucepick]

I found LRR tires to definitely give better mpg. Whether it's worth the cost for your particular car and tire size, try do some math. Estimate a couple mpg increase and see what you come up with.

I can't say how much mpg increase you'd get but I know it makes a difference.

As for whether tires would rub or not -
Bigger rims don't determine overall tire dimensions. That is determined by tire size.

The deal is to get the same size outer circumference as what your car had for stock. You need a tire size calculator for that, if you are changing tire or rim size. Or a decent tire place like tirerack.com will tell you what sizes will fit. As for the width of the tire, I think tirerack will tell you that too. And/or you can try find out the biggest "performance" tire size that GM ever sold for the car. That would be your max width.

Also you can put your hand inside the wheelwells and feel around to find out how much extra clearance there is. Remember to account for wheels going up + down, and front ones turning to steer.

I'm not suggesting you put on tires of the max possible width - because skinny tires are usually better for mpg. But you might not find skinny ones available and might have to get something a bit wider.

If you can get tires rated for 51 psi pressure instead of being limited to 44 psi, go for it. Once you get a taste for highly pressurized tires you won't want to be below 45 psi again.