Our use-case is to use a Single TCP Connection (never close) and perform a request-reply model, while the next message waits until the reply is received for the current request (block mode). Should we consider 60 messages / min as Low-Volume or High-Volume, this will help us determine whether to use a Gateway or pair of Adaptors. Thanks
That would not generally be considered to be high volume, but only you can determine which architecture provides the performance you need.
e.g. the 60 messages come in 5 seconds and then no messages for 55.