I havent heard of the heads warping. Though, i did have to replace the head gaskets at 55k miles.
I have a 318 in my ram, and i get about 10-13 mpg. I got 15 once doing 45 on the highway.. but then this is in a 5500lb truck on 33" with 3.55 gears.
I wish i had the heart to sell it because i sure would like a TDI VW to cruse around in.. 10mpg HIGHWAY gets old quick
BTW, i have 90k on my engine, and it used about a quart every 4500-5000 miles... which is when i do an oil change anyway.