I have looked into this and I think the answer is 30-40% probability of upgrade from a 6 to 7 depending on the study.
It's a bit strange, but my husbands biopsy result was exactly the same as your 3+3, 1 of 12 cores at 10%. His post surgery pathology was 3+4, organ confined and a relatively small cancer. What was particularly shocking was that there were 9 seperate areas of cancer.
We are now nervously waiting for the first post op PSA results tomorrow.
Hope this helps.
An