From fuel prices to tax credits, which hybrid pays you back?

Lexus RX 400h
Hybrid FWD

Base Price (inc. dest): $42,345.00
Tax Credit $0
Adjusted MSRP: $42,345.00
Premium:  $3,880.00
MPG: 27/24 (city/hwy)
MPG Benefit: 5
Combined MPG: 25
Annual Gas Cost (15,000 miles, $4.20 per gallon):  $2,520.00
Gas Savings:  $630.00
Years to Payback: 6.2
EPA Pollution Rating: 8
Compared to: 2008 Lexus RX 350
Base Price (inc. dest): $38,465.00
MPG: 18/23 (city/hwy)
Combined MPG: 20
Our Take: “Surprisingly peppy performance from a feel-good powertrain, this quiet-runner will be a favorite in upper-class suburbs.”

Details, Price Quotes:
Lexus RX 400h Hybrid