Both of these cars are an absolute thrill to drive. The V is more fun than any vehicle I have ever driven. In the end I chose to buy the G8 for a few reasons. The first is price. I got a stupid low price on a G8 that had gone home for the weekend with some one and came back on Monday when they did not qualify for the loan. The nose had bottomed out and had a 3 inch gouge in the underside and there was a door ding. All this with just 150 miles on the car.
The second reason is the interior room. While the differences are just inches, the rear accommodations are huge. Sit in both and you will agree.
The third reason is Utah. We have had some hard snowy winters and there is a lot of sand and salt used. If I had the Caddy, I would leave it in the garage till the sun comes out. Having that attitude, I would still be waiting for the snow to go away so I can drive. The G8 is an everyday car. While I still hate the weather abuse, I can put up with it.
The final reason is that I love to wrench on cars. The G8 affords tons of opportunities to build the car into a vehicle with tons of power and track ready. The V is the king. It has it all and I don't think I could do much to make it better. I drove tons of laps on the Monticello track with the CTS V, XLR V and standard CTS. It was the most fun driving day of my life without a podium finish. The car is flat out amazing with more luxury than any euro sport coupe could hope to have. (Well the M5 is close).