Actually you are wrong Deca will NOT clear in the same time.
http://www.medsafe.govt.nz/profs/datasheet/d/Decadurabolininj.pdf The metabolite life in the body is about 3 weeks at a pharmacological dose. The pharmacokinetics display that the half life is 6 days and the cleaved compound (once removed from the ester) is only active for a 4.3 hour period. This is after it is absorbed from the oil depot from injection and takes place over a few days in supra physiological doses (past 50mg). A 50mg dose is used to treat women with a carcinoma or osteoporosis in men or women.
So your idea of when to start pct is off. Yes deca and test have the same active life and half life in the blood but not metabolite life. Circulating metabolites can continue to suppress the HPTA function. They are NOT the same length ester one is a decaonate ester and the other is a Enthanate. The STEROID has the same halflife but ester lengths are different. 3-4-500mg IS a low dose considering medical studies are in the 50-100mg range. To build mass you need to almost triple that over a 12-16 week period. So 400-500 really isn't extreme for a average sized man. Get into the 220-250lb+ range of bodybuilders and the doses are in the 800mg-1.5g range ew.
Please show this study that you will lose collagen synthesis at over 200mg ew. I couldn't find proof of this theory. Of course there is a synergistic effect. Test is needed for basic function in the body to maintain a anabolic to androgenic ratio.
Any steroid when used with testosterone is synergistic in nature. Deca should ALWAYS be kept equal to or even better... Lower than test doses because of it's ability to produce elevated prolactin which will bind to the progesterone receptor and effect your dopamine levels resulting in the feared "deca dick". That is why a long ester testosterone like Enthanate, cypionate, sust or nebido is recommended.
Please educate yourself before you post "data" that you believe is true. False information and bro science are just as bad if not worse than no information.