I think you have to look at a lot of things beyond the simple things you are considering:
For me I got the loaded V6 after test driving both. Here are the reasons why:
Gas Cost: For an average driver the V8 will use 114 gallons more gas per year. In the US this will cost you about $400 more per year. In Canada where I live it will cost $600. And what about when the gas prices go up.
Insurance: For me the V8 was $120 more per year.
Tires: Replacement Tires for the 19's vs. 18's will cost about $300 more every 3-4 years. So about $90 more per year.
Winter Tires: The V8 needs 18" winters where the V6 can use 17" due to brake size. A good set of winter in 18" low profile tire with
rims is about $600 more than 17". My winters last me about 6 years. So about $100 per year. This will not affect those in warm climates.
Initial Cost: V8 was about $3000 + tax more in cost than V6 for me in Canada. Over 10 years over ownership is at least $300 per year.
So I predicted for myself that the cost of ownership of the loaded V8 vs. loaded V6 to be about $1,210 per year for the next 10 years if I keep the car that long.
With the V6 being as powerful and smooth as it is, it was not worth $1,210 per year for me to have the V8.