I run my treadmill and find that I am slower on it than out side..it is nice to know how far and fast you are running but I prefer to run out side. I have selected several types of runs where I knwo exactly how far I use the previous time as a base. Some are flat and fast some hillly others offroad..Everynow and again I go to local track and blow out a mile just for fun.....
Treadmills were made to prevent you from losing it all not a good primary training tool, or so I say.