You're going to get a lot of varied replies as each model and generation has different engines, gear ratios and power bands. For me with my C7, and I would expect for many others that it depends totally on the road, your state of mind and traffic. If I am on a longer run major divided 110 kph 4 lane highway that is a straight line and want to have a nap while driving, I will set the cruise at 125 and drive in 7th at about 1350 rpms. Most of the time though, my boring straight highway driving for fuel efficiency is in 6th. On a lower highway speed limit or hilly road, I never use 7th and seldom 6th. On a 100 kph 2 lane road with traffic slower than I want to drive and I am passing at every opportunity, I will likely be having fun in 4th and close proximity to 3rd for giddy up and go passing.A poll question. Do you drive at 2500-3000 rpm in 4th gear or 1800 rpm in 5th. ?
Seems to me like a rock and a hard place.
As others have also said, with the C7 I put it into 7th if I'm putting it on cruise control between 100 and 120 KPH...may as well save engine rev's & some fuel. I did the same with 6th gear on my C5. I still think back to the days of my 78 C3 with a 4-speed, no o/d - I had an L82 with a 3.7 rear end and it revved at 3,100 RPM at 100, and 4,000 at 120. No a/c...so it was NOISY on the highway. The C7 in 7th rev's at 1,300 at 120...you can actually have a pleasant conversation with your passenger without shouting.A poll question. Do you drive at 2500-3000 rpm in 4th gear or 1800 rpm in 5th. ?
Seems to me like a rock and a hard place.