I have driven a few miles on disel cars, but never owned one, so no real experience. I don't think diesels last longer just because they make their power at lower RPM, but because of the people likely to drive it. Every car advertise "highway miles" . Oh yeah, I put 100,000 miles on it, but it was all "highway miles", no worries

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I think with most diesels, that's actually true. I think most people get diesels to commute or for commercial transport. I think most diesel owners are not red-lining their motors. I think most diesels owners consciously make the choice for diesels, probably actively take care of their diesels and are the kinda owners that make whatever they own....look good.
I think even a gas motor can get to 500k with little trouble if you drive within the engineered limits. I have friends with big turbo diesel cummins truck that didn't make it to 100k miles and I have friends with gas toyotas that were over 300k on the same drive train. I myself had a 200k+ mile gas powered VW.
Honestly, I think proper regular preventitive maintinence, driving behavior and "highway miles" has more to do with weather a car gets to 500k, be it diesel or gas. Granted, there are more diesels out there that are 500k+, but those are probably all commercial vehicles, highway driven and regularly serviced by real mechanics. Things that make it so you need a new long block at low miles probably has to do with abuse and neglect of the motor.
I am not sure a TDI is more responsive then gas. Pretty sure a 0-60 time for a gas will far exceed an equivilant TDI, lets not even talk top speed. However, I don't care. I drive around the speed limit, I accelorate smoothly with more concern to fuel then anything else. A better tow capcity would be great. Yeah, the diesels are more inline with what I want and I'd opt for it, I just wanted to point out that for the money, gas doesn't compare poorly and has the potential to last a long time too.