Since this is a perf PR, I think it'd be nice to see some benchmarks to be absolutely sure.
Answer to this is “database specific and depending if there is an index on the column or not and how that index is organized”,
some database-storage engine-index type combinations will opt a full table table scan instead of index scan/fetch when “between” happens as opposed to a “=” query which would imply severe performance degradations in specific cases. Perhaps this can be addressed at adapter level or as a configuration option?