Help me decide (dual sport)

18 y/o, 6’2”, 34” inseam. I’ve only ridden small dirt bikes so far. I’m taking my endorsement class in March.

Main plan: explore nature, hit forest roads, try some trails, and find cool places out in the mountains. But in Montana I also have to do 70–80 mph highway stretches just to even get to those spots.

Budget: around $3,000 cash. I could put $3,000 down on something new if it’s worth it (was looking at a brand new DR-Z400S but ~$8,000 is a lot).

Shortlist right now: KLX250 vs DR-Z400S.

Question: Would a 250 suck at 75–80 mph highway cruising even with gearing changes? Or should I just go 400cc+ from the start?

Looking for reliability + not screaming the motor on the highway, but still capable off-road for trails and exploring in nature.