efficiency/lugging question

I'm unemployed and considering taking a job which would have me commuting on the highway for 24 mi each way. Roughly 15 mi is a 65 zone and the rest is 55. I ride a 2015 KTM 1290 SDR and right now gas price is a concern.

If I want to go 70-75 in the 65 mph section, should I use 5th or 6th gear? I assume 6th gear would be more efficient but I'm not 100% sure. Also 6th gear at these speeds does feel like I'm lugging it. And when trying to go actually fast 6th gear seems utterly useless on this bike lol. It's not flashed. Based on advice from Ryan at FortNine, it seems like I should always keep the engine above ~4.5k rpm. 70 in 6th gear is maybe 4 or 5k rpm. I can accelerate in 6th gear even if I'm going 65, but it accelerates pretty slowly.

5th gear at 70 really doesn't feel like revs are higher to the point that it would cause extra wear, but I do imagine more strokes/min means more gas/min too.

Curious what your opinions will be. Am I over-thinking this?

Thank you!