You don't have to worry much about estrogens if you go the transdermal route rather than oral with testosterone.
Up to 100mg/day applied on the scrotum for 10 days didn't give me any high e2 symptoms, which means the DHT increase is completely sufficient to counter them.
Estrogens are not the devil, as long as they increase proportionnally to your androgens.
Also, you took T and P5 together. How can you be sure what caused what?
I take T for about 3 month now, and only have started the P5 a few days ago. Thats how I am able to differentiate the effects. I think you are right that at 100 mg estrogenic sides are very low for such a high dose, which is quite amazing. I stupidly used 200 mg some days, using 100 mg as a pre-workout, and I got some supposed estrogenic sides like slightly enlarged breast tissue then. That is gone now tho. There is quite a bit of adipose tissue on me so it is pretty cool to be able to avoid way high estro.
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On an unrelated note, I think my hematocrit got way too high (or rather my blood thickness), so I am taking at least 1g of aspirin or Vitamin E daily and that seems to help. Still have to donate some blood I think.