Also depends if you're just counting your pocket, or the environment. But I agree with the analysis you posted.Not so fast; in the past few years the price of premium has risen precipitously, with the end result that at most gas stations today, premium is now a full 60 cents/gallon more expensive than regular unleaded.
So for a trip of 300 theoretical "combined" miles, according to the EPA:
3.6L: 20 MPG, so 300/20 X $2.59 (local price for regular unleaded) = $38.85
2.0T: 24 MPG, so 300/24 X $3.19 (local price for premium unleaded) = $39.88
The 2.0T would need to beat 24.6 MPG just to break even, and let's not forget the 2.0T engine will probably cost more than the 3.6L.