Went from racing 2 miles in hs to 5 miles/10k in college. I preferred 800/1500 in track as I was much more co.petitive at those distances. Still loved summer miles and road races of all distances from 5k to a full marathon.
It took 3 years of solid training without injury to adapt to 70-90 mpw for College XC while still competing 800/1500 indoors/spring. Still loved the grind and couldnt believe the impact the miles and strength gains of XC on my track results. Still not top 7 on the team until I bought all in at 90-100 mpw. We had a good team and qualified for NCAA D2 meet. 30:10 for 10k. Nothing spectacular but good enough to make our top 7 and finally contribute. Continued to sub 1:50/3:50 in the spring.
Without a doubt: XC made me better in track. Couldnt have done it without an understanding coach and my teamates dragging me along.
Fast forward about 6 years...... Still before the internet.
My hs girls team changed over from 2 miles to 5k in our state. I told them the night before their first race because i didnt want to lose recruits or scared veterans. They were mad at me but i reminded them of their summer mileage gains, their long runs up to 10 miles and the gut grinder fartlek, interval and tempo workouts we had done with many easy days in between. I told them they were ready for it and i was certain most others werent because they were already mentally defeated. My girls proceeded to dismantle the field in short order and continued to do so for the most part for the remainder of my time at that school. They were built tough and they knew it. It takes time to grow a garden but hard work still beats talent on most days. Patient coaches can teach others how to approach new challenges.
So yeah, maybe keeping 6k until regionals and nationals then 8k would work better for mai taining numbers and then let the true distance athletes rise to the occassion. I was a Mid D guy that needed more time to prepare but I loved every mile of it. I stayed home a lot for 3 years and ran road races until I was ready but I finally got my chance. Hard work beats talent most days. Its those darned talented, hard working sorts that make up that top 10% that are just tough to get in front of.