I believe temperament is dependent upon the individual. I have found very defensive (not to be confused with aggressive) individuals within all Drymarchon subs, and I currently maintain all subs within my collection.
I have yellow-tails who are very defensive and will not hesitate to bite, sheepish individuals who will demonstrate no defensive behavior while reaching into the enclosure and picking them up, but will simply turn their head during handling and clamp down upon you and a few individuals who are simply none defensive.
I have a single black-tail, which will act more like the sheepish yellow-tails and unsuspectingly clamp down on you, but my other three are as docile as can be. I did obtain a WC individual once, which was highly defensive and would strike at anyone passing before the enclosure.
I have Texas Indigos which are either very docile or highly defensive, no sheepish individuals there and they readily let you know who’s who.
The Eastern Indigos I have, are quite tame, have never acted highly defensive, other then to vibrate their tails when upset, and have been among the most bold, yet docile snakes within my collection. I have captured D. c couperi within the wild, in So. Dade Co. Florida, many years ago, and even they never offered to bit. My worst experience with a wild caught involved flattening of the head, tail vibrating, salivating and of course excreting musk and other bowel contents. Most would simply allow you to approach and pick them up, without attempting to flee or acting defensively.
The Unicolors I have are all very docile, rarely, if ever, act defensively, but are a bit more secretive. While I have never been bitten, I know of an individual who recently experienced a bite, from a very large specimen, during a feeding accident, which sent him to the ER for sutures.
My Mexican red-tails are a diverse bunch, while none are very defensive, I have a large female who is of the sheepish nature and will just clamp down on you without warning, a male who acts in a very defensive manner, yet will not strike or bite and another female who is VERY docile, except at feeding time.
The best advice I have, is to acquire a captive bred specimen of any Dry sub you wish and interact with it on a regular basis, after you have given it a few days to acclimate to its new home.