This is my first manual car so excuse me if my terminology isn't that great!

I just bought the car 3 months ago, it has 130k miles and I'm the 2nd owner. I've mainly been driving it around town and a bit on a highway (but not above 65mph)

My dad taught me to drive by listening to the engine to know when to upshift/downshift but I've also been looking at rpms. If I pay attention to the rpms I will shift up at 2.5-3 and downshift when the engine sounds bogged down/rpms are below 1.5-2

When driving, 4th and 5th gear seem EXTREMELY short. I will shift up into 4th at 40mph/3rpm and then have to shift up again to 5th at 50mph... Seems really short to me or am I wrong?

Additionally, I take trips on a toll road where the car will need to go 85-90mph for a good 2+ hours. But the way 5th gear sounds, she won't go above 70 without being very loud and rpms being up in the 4's. Which according to what I've read, 4rpms isn't that bad but if I listen to my dad's advice then the engine sounds awful and needs to shift up (but I can't since it's a 5 speed). I guess the question is, is it okay to drive the lancer at 85-90mph even if the engine sounds awful? Is it normal for manual transmissions to be that loud? I feel like even if it is okay to drive the car that fast for that long, the higher rpms are going to kill my mpg...

Any advice is appreciated!