Actually, novadex by Gaspari contains 3, 17-Keto-Etiochol-Triene also known as ATD. This is a potent suicide aromatase inhibitor that can give estrogen suppression close to arimidex.
Back to arimidex v. femara
http://jco.ascopubs.org/cgi/content/abstract/20/3/751RESULTS: Pretreatment aromatase levels ranged from 1.68% to 4.27%. On-treatment levels of aromatase were detectable in 11 of 12 patients during treatment with anastrozole (mean percentage inhibition in the whole group, 97.3%) but in none of the 12 patients during treatment with letrozole (> 99.1% suppression in all patients; Wilcoxon, P = .0022, comparing the two drug regimens). Treatment with anastrozole suppressed plasma levels of E1, E2, and E1S by a mean of 81.0%, 84.9%, and 93.5%, respectrively, whereas treatment with letrozole caused a corresponding decrease of 84.3%, 87.8% and 98.0%, respectively. The suppression of E1 and E1S was found to be significantly better during treatment with letrozole compared with anastrozole (P = .019 and .0037, respectively).
CONCLUSION: This study revealed letrozole (2.5 mg once daily) to be a more potent suppressor of total-body aromatization and plasma estrogen levels compared with anastrozole (1 mg once daily) in postmenopausal women with metastatic breast cancer.