Although I have found these tools before - the accuracy depends on you.
I use VDOT for the same thing -
but lets say you are to improve 30 seconds per mile, that is maximum, then you have to apply your running effeciency (Like the effeciency of a transmission to transfer horse power to your drive system)
Not many of us have perfect effeceincy, so I usually get about 1 second per mile per pound loss -
