A Rav-4 at $4/gallon will cost $227 more per year as a 6-cyl than 4-cyl if driven 15,000 miles per year. The difference is about $140 per year now. If the extra power is meaningful, you can now put a price on it. BTW, that’s less than $2.50/week now. Drive them both and decide if the extra power is worth it.