I bet you felt great the first month on 300 MG's every 4 days. Honestly, in all likelihood, you would've felt similar if you had taken 50, 75, 100 MG's every 4 days. Initially taking exogenous testosterone, especially if you had low, or very low testosterone levels. But after a month or so, your body will adjust, and that "testosterone honeymoon" will end. Not saying you'll feel bad or won't still see major benefits, but you most likely will not stay feeling the same way you did the first 4 weeks. Also, by the fourth week, especially on enanthate or Cypionate, you're other hormones will have been affected, including estrogen, prolactin, etc...and the higher your testosterone dose, the more these other hormones will be affected. On 300 MG's Testosterone every 4 days, almost 600 MG's weekly, your estrogen levels will undoubtedly rise and start causing you issue's if you aren't taking additional drugs, such as estrogen blockers, inhibitors. You're also going to most likely see significant lipid issues with your Cholesterol numbers. Your HDL and LDL numbers will change making you more at risk for coronary artery disease. You may also start to have issue's related to your prostate with your PSA numbers rising and your prostate growing larger possibly causing urination problems. ED and difficulty/inability to orgasm may start to arise as your other hormones get out of whack if you don't take additional medications to keep them in check. 600 MG's Testosterone weekly is definitely not considered TRT and I don't see any clinics or Urologists prescribing that high a dose, especially longterm.
I'm definitely not casting judgement as I've done what you're doing, and a shit ton more, but I am trying to let you know it's definitely "not all roses".