i'm 30 and have been on HRT since August '06, currently scripted 200mg cyp ew. I've been bumping to 250 the past couple weeks, and don't notice much difference...I'd go for 300, but I'll run thru my scrip alot faster and I don't want to piss my doc off so I need to get approval.
My doc says that if I want to have kids, he will probably take me off the test for a couple months and put me on HCG. My natural levels weren't awful, but I seem to have a high affinity for test. Even at 200mg ew, my total T just prior to my next inject was just over 500. I've heard some people say that they're near 1000 at this point from only 100mg ew.
Doc says there's a new test coming in '07 that measures the effectiveness of one's androgen receptors and this will explain why some people need more T than others to achieve the same results.
In the time I've been on HRT, I've put on 22lbs. Mood, sex-drive and energy have all been awesome. In the end, HRT's been awesome to me. If I have to stay "on" permanently, so be it.
Good luck.