The mazda 6 shouldn't be considered being able to race a gts. 6 cylinders or wathever, the 6 hasn't much of a sport car. Weight does matter. Same goes to handling caracteristics. Plus, this car doesn't really pull IMO. from what I've seen at the least. Kindda like all those heavy american cars with 6 cylinders that doesn't really pull (not to generalize, not all are like that). Yes, they have torque and are easy to drive. Yes, most people want hem. But, I admit, there face are priceless when you walk on hem easily with a little NA 4 banger. By their faces, you know they thought they would be able to compete. Hope to see more easy kill like that on the streets hehe!!
If your not able to pull a mazda 6 in a gts, you don't diserve a gts. Period.
Peace!!