Sure, to make a backup before a coverting process is better, if a convert is possible. But only a backup is much better than a backup and restore of 2 TB of data. The backup takes here 30 hours to a LTO1 drive...

I think that the higher data transfer rate will be result in a better performance because the time for the data to went from the target to the initiator is smaller.

All this is depending to the performance of the raid too, i know...