There is a thread by Eddy Lee about breaking 4 minutes and your times are not much different than his. Judging from you 800 time I suspect you should be able to run 4:15 or so in the mile. This is not a great sign for you. I am concerned that your 1000 time is already showing signs of slowing to a degree that maintaining your speed might be a problem. I would want to see a 400 time and know more of your training history. Without an indicator that you have sprint speed or that you engage in minimal training, I would guess your probably close to your potential.
That being said, I am never one to say don't give it your best. Will is an amazing asset. Best of success to you.