Duplicating 9940 to LTO4

Hi,

we need to duplicate a few hundred 9940 tapes to LTO4 media and am looking for the best and most efficient way to copy the tapes.

My other question is:

9940 are based on NBU 6.5 and this has to be duplicated to LTO4 based on NBU 7.6. Will there be any issues? 

I will be using vault. Is this the most efficient method? Also, what is the time estimate to complete about 100 tapes.