As for what you said previously, i feel a little confused.
The buffer memory is used as a cache on the device but you would need to ensure that enough data can be transferred to the PC to avoid the memory from becoming full and thereby losing data.
In the quote, do you mean that effect is for the block mode ? As far as I know, when it is transfering data the scope stop collection and start again until the transfer is finished. so i think the transfer rate only effects time interval between captures in block. Therefore ,i am really confused that it might bring data losing.