I think it will be great if there's something like paste-transfer-queue to be an option, especially when the multi paste have a same target. The way Dolphin handle it now, it transfer simultaneously, causing slow transfer rate. 
For example, I want to copy file "X" from my /home to my flashdisk, then I just realize that I need to transfer file "Y" to that flashdisk. Because the write speed of that flashdisk is slow, the simultaneous transfer make the write speed even worse.
It's great that the copy-paste dialog have a pause feature, so user can use it to make one time transfer only by pausing the other transfer, but sometimes the transfer rate still as slow as simultaneous transfer.

Reproducible: Always

Steps to Reproduce:
1. paste a file to a device (for example, flashdisk)
2. paste another file to that device when the first transfer isn't finished yet
3. pause the second process, wait for the first to be finished, then resume it
Actual Results:  
the transfer speed will be divided to the multi-process, but pausing one process won't restore the transfer rate.

Expected Results:  
if user have press the pause button, the transfer rate should be restored (not cut in half). It will be better, if there's queue option for such task.