Estrogen, in sufficient quantities, just puts the breaks on testosterone production (through negative feedback loop). That's what causes feminising effects. Its not the estrogen itself that feminises. Transexuals often use anti-androgen compounds (like spironolactone) for the feminising effects. I don't think increasing estrogen to very high levels even has the capacity to fully feminise a male if his androgen are still high enough. Many men have very high estrogen but still look like men.