I’m not sure you’ve really provided us with enough info to answer your questions, but I’ll try.
I run on my treadmill quite a bit and here are some things that come to mind. Treadmills are notorious for not being calibrated correctly. My HRM usually doesn’t work properly when I’m on the ‘mill. I find I can usually run faster on the ‘mill – meaning a 6mm on the is easier than on the roads. So people say you should increase the elevation to 1 or 2% in order to mimic the conditions of running outside. Check out Ryan’s link under “training” to the far left.
If a 6mm only put you at 180, you must have been around 120 for that 9.5mm. Seems like a really strange workout, especially if you have a coach telling you to do that.
#1 – As for breaking 5 minutes, it’s hard to tell. There’s a big difference in those 60 seconds. However, if your mill is accurate and your HRM is accurate, I’d say you could probably break 5 minutes if you focused on it.
#2 – Like I stated above, it’s probably harder outdoors.
#3 – Sort of depends on other things like sex, age, etc. Sub-6 for high school is very doable for boys and girls. The majority boys that run x-c and track at that age would also be able to break 5:00. I ran a 5:01 1600 in high school. Now at 35, I’m a much stronger runner overall, however, it’d take a lot of work for me to get back the speed needed to run that time again. I don’t want to “waste” my time training for such a short event.
Again, those 60 seconds between 4 and 5 minutes are big. I can’t rattle off the top 1500 times in the US last year, but I’m sure you had to be quite a bit under 4 minute mile pace to make the Olympic team.
Do you have any running goals? Why does your coach want you to run if you’re a cyclist?