Among Boa Constrictors (excluding Anacondas), as a general rule, the true red tails produce some of the largest localities - Bcc Surinamese and Guyanese are the largest localities with males reaching 7-9ft and females often reaching 10 feet or more.
Argentine boas are also very large, being heavier bodied than most other sub-species. Females are often over 8 feet.
Some Colombian Bci females can get quite large as well.
It is important to note that any sub-species and/or locality can produce larger or smaller specimens.
B.c. sabogae and nebulosa are actually two of the smaller sub-species. Sabogae are an insular sub-species and nebulosa are a mountainous sub-species.