The EFI version CUltus has mechanical valve lifers which are slightly noisier than the hydraulic lifters that cultus 2006 had.
Thats the reason hydraulic lifters were invented in the past to reduce the click noise when the lifter engages a valve.
So this acounts for Noise problem. Its perfectly normal unless you could hear something odd while sitting in passenger cabin.
Regarding RPM vs speed, both versions have different gear ratios. The ratios are design based on engine torque characteristics. The 3 cylinder carby G10 has a different characteristic than a 4 cylinder efi one.
On highway cruising speeds, the gears are designed to keep any engine around its torque peak to minimize response lag under load.
I have owned the 3 cylinder version in past and have traveled quite a bit (officially) in the 4 cylinder. And I used to compare these two things myself. Its normal.