[mdbrjb]

Just a couple of thoughts.

1. The new Tacoma's with the 2.7 four are turning only slightly higher rpm's than the 6 when in overdrive.

2. Because an engine is at higher rpm's doesn't necessarly mean it's working twice as hard or wearing twice as fast. The wear is determined by load (heat), not rpm's. People pulling trailers with their 6 don't use overdrive so they don't load the engine excessively. In many cases, low rpms are harder on the engine than high rpms. I can pull my little trailer in OD, but it's easier on the engine to do it in 4th.

On average, from what I've read, in most circumstances there is about a 4 mpg difference between the 4 and the 6. I don't think this is enough to really make a big difference.

I think that the biggest determining factor on how long either will last is really going to be based on how you treat it. Frequent oil changes and not beating on it will really make the difference.