I can get well over 600km's per tank on the highway with my I4 MTX, with my V6 MTX it is more in the neighborhood of 525km's per tank. That would be doing around 130kmh. Not very sure about the ATX but it's final drive gear is bigger so in theroy it would get slightly better milage on the highway. Hope this helps.

hunter green 96 mystique mtx, sabb side markers deep tints
car bra., K & N filter, hyper white low beams, after market fogs, JVC Kameleon head unit, 600 watt amp with 2 10" kicker subs, soon to come new rims

New adition 01/11/2002 The original 95SE in Midnight Red all the toys including traction control
Fog light mod, lightmoonroof switch from a focus, power antena (still wiring it up) post 98 sail panels, new water pump , Bosch quad plaitnum plugs, and a new Cat.