As the earlier reply mentions, there is no right answer (also varies between the 8 Oneworld FF plans), but ballpark is 70K miles for a reasonably aggressive DONE4 with elapsed time of a week (unless starting in area 1 which has a 10 day minimum duration requirement for all xONEx fares). Remember that some routes are seasonal or not daily, complicating planning. For fun I wrote some route selection software and the longest DONE6 it could find was something like 90K miles under the current rules, however it was a routing that I would never fly willingly. That should bracket your expectations (and illustrates how the OWE fare is quite a bit more than a RTW of 25K miles, more like a double RTW).