Yes.
You can go from 6.5 to 6.7 directly. Time is related to link speed and hardware performances.
Data in shared folders is not modified in any way, it can't be lost.
You can restore a backup coming from 6.5 in 6.7.
I agree with you that the whole process should be tested at least once. I've completed a lot of updates without issues, my confidence in the process is above the average. 