I assume that you mean the limitation of TRTH V2 in DSS. In TRTH V2, there is no gzip file size limit. For more information, please refer to this question.
For downloading, users are allowed to have up to four connections. Download speed for each connection is up to 1 MB/s.
How to extract instruments from instrument list using REST API endpoint mentioned here API tree (https://hosted.datascopeapi.reuters.com/RestApi.Help/Context/Operation?ctx=Extractions&ent=InstrumentListItem&opn=GetAll)