Oncologists are usually seen if there are some complications with your therapy but they are great to see if you can for a true unbiased opinion on which way to go as inital therapy is involved.
If you truly have some high Gleason scores like you think you do you should do your DD but don't wait around too long making a decision. Us high Gleason guys need some therapy sooner rather than later.
Some other things to consider are how many sticks were positive and what percentage of each stick on your biopsy. What is your staging T1c or such, it all matters in your decision making.
David