Diff ratio help

2.92 first gear, 0.8 5th gear, 0.63 6th gear. Rear tyres are 26 inches, haven't got dyno results yet and I don't want stupidly low revs on the highway - about 2000 - 2100 at 65mph is about it. With 650 horses, 5th gear is a power gear at 65mph if I want to overtake, but I love 4th for doing it in a quarter of the time. Sixrh gear is just a waste of a gear, unless you want to save on gas travelling freeways. I'm happy to use the gears, it's why I got it, so good cruising RPM at 65mph is what I'd like. Sounds like 3.7 to 3.9 would be much better suited to my needs? 3.9 more so?
10:1 ÷ 2.92 = 3.42. Mopar has 3.55 ring and pinions.
2.92 × 3.73 = 10.89:1 With that power/torque and this reduction it will be real easy to burn the hides.
2.92 × 3.91 = 11.42:1. First is almost useless.