If that is the case, I guess it isn't a real problem cruising at that rpm other than the higher volume of noise that the engine is making.Hmm no, highway driving still more efficient coz even though 4000rpm but it's cruising, not accelerating as often like town drive. I can see that on the econometer.
It came with the first version of Dunlop Sportmaxx which is a pretty good UHP tire also, I'm testing it now and still works fine despite the age already >10yrs old! I also saw on some other car that came with Goodyear F1A2 which is even better.
Wait? The tyre model's age is over 10 years old or the set of tyres itself is already more than 10? If it is the tyres itself, wouldn't it be better if you replace it due to age?
A question of curiosity, have you tested a normal Swift before? The same generation as your ZC31S. If you have, I wonder about the difference in handling?