Thats a fairly large amount of data your dealing with then, if its multiples of 1gb in a CSV. May I ask why you need to split it into multiple files. A couple of other ideas:
Generate one CSV and stream it via HTTP
Generate one CSV and ZIP that using the inbuilt function of WinZip/RAR to split the archive into chunks of 1gb
Reassses if you really need to send that amount of data, what is the purpose of it, i.e. if they are just summarising it, why not summarise at your end and send the summarised data
Can you compress the data in any ways, for instance code longer text strings into small numbers, and provide a code list or formats catalog with the data - you would be amazed at the amount of storage space saved merely by changing a 20 character string into a 3 number coded value.
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