That is a difficult question to answer but hopefully I can give you a general idea. Conversions never actually stop happening in the body as hormones are constantly moving back and forth. They have done blood incubation studies but in reality they dont tell to much about what is really going on in the body.
These are a couple of good reads on the topic:
1.
Invalid Link Removed - Discusses the benefits of sublingual PH delivery. This includes a reference to a 4-Adiol study that increased test levels 261% with 25mg's.
2.
http://anabolicminds.com/forum/steroids/133635-pa-conversions.html - A better idea of what "conversion" means and how/why it is difficult to answer these questions with exact numbers/references.