One of the reasons the dive goes/feels much better is because the urge to breathe is postponed. If CO2 cannnot be buffered by storing it in muscle tissue, as with a stress-induced peripheral vasoconstriction, for example, then the PaO2 (in the blood) will rise very quickly; similar effects can also result by descending vey quickly through the water column without first hyperventilating and/or warming-up the muscles. This can result in a very strong urge to breathe referred to as the "uglies".
For serial diving, where it is the aim to have a rapid turn-over of dives, thus maximizing underwater time and reducing fatigue, it is important to maintain patency of blood flow to the working muscles, e.g., locomotors. Enhanced blood flow to such muscles will help buffer the CO2 but will, however, also lead to a much more rapid usage of O2 stores. So, although being relaxed is conducive to efficient serial diving by preventing excessive build-up of anaerobic waste products, the urge to breathe and prolonging recovery duration, it will also limit dive duration. This is why, when serial diving it is crucially important not to seek to set any records and to ascend when the urge to breathe first arises. The problem is that many divers , even world record holders still mistakenly believe that their best performances occur when they're relaxed and warmed-up.
On the other hand, although cold-water and stress (e.g., no warm-up) will result in an earlier urge to breathe than when relaxed and warm, PaO2 is maintained higher for longer. Unfortunately, however, this means that muscles must rely on a limited blood flow (=HbO2) and intramuscular O2 stores(=MbO2) for efficient functioning. Because O2 stores are severly limited to working muscles under these conditions, they will have to predominantly rely on anaerobic (without O2) energy stores -> muscle fatigue, long surface recoveries. Although this is not a cost-effective way to undertake serial dives, it is by far the best and most intelligent way to set personal bests. Fortunately, the fatigue is only localized and does not result in a quickly developed and excessive urge to breathe, since the build-up of CO2 in this instance is largely due to vital organ metabolism as opposed to muscle metabolism. Remembering of course that in this instance the urge to breathe is centrally (where blood flow exists) instead of peripherally (where the muscles reside) located.
From experience, doing literally thousands of controlled trials over the years, I suggest that divers go dynamic (=ascend) when the urge to breathe results. Typically, that ends up being a 1:1 (descend:ascend) ratio. A 60" free-fall, for example, may only mean reaching a depth of 35-40m. Of course, with descends taking longer to effect than ascents, as they are undertaken passively, it means that one only needs to ascend, perhaps for as little as 40". That being the case, the 1:1 ratio is a conservative one, especially if depth is achived before the urge to breathe arises.