Rob,

I remember reading a recent post of yours which sounded like a nightmare (for the cars and yourself). Something about running dino 50-weight in some of the cars, and 10-30 in others.

Why not put the same thing in all of them, then compare again. Since you sounded like you're a dino-phile, the Delo 10w-30 sounded like the best of the bunch. If not, you can get 5-quart jugs of Valvoline or Mobil 1 synth for $12-15 at Wal-Mart and clean those long-suffering motors out.

Also, what's in your diff and tranny can make a diff. After I changed them to synthetic, my car was just slightly snappier, and also slightly quieter. And--it still makes me grin--it shifts easily when cold. Only gained about 1 mpg, though.