No Preference given to tatkal ticket holders.
Tatkal wait list & Gen Wait list are two different type of wait list & working independently from each other. So No issue of priority.
But yes people have wrong impression in their minds that having tatkal ticket(by paying more amount than gen ticket) they will be given preference over gen wait list. While it is not so.
Tatkal...
more... wait list moves only when a passenger ahead of you in que in tatkal quota cancels the ticket & Gen Wait moves only when a passenger ahead of you in que in gen quota cancels the ticket.
If there are some non utilized quotas remained at the time of charting First it will be alloted to Gen Wait list.
Some say the preference to allot non utilized quota to different type of wait list is as follow
1) GNWL
2) RLWL
3) PQWL
4) CKWL
But I personally observed it is not so. Although Gen Wait list enjoys priority over other wait list quotas to get non utilized quota but I think there is fixed ratio to allot these quotas to each type of wait list but what it is I am not sure.
Good Wishes.