It wasn't a poll, but I queried forum readers on this a while back (link). A few responders indicated that they were XMRV+ and had POTS. My question was not as comprehensive as your four possible cases, however.
Hopefully the big survey effort will end up revealing a lot about these sorts of questions. Mrs. subtr4ct has POTS, and we are awaiting VIPDx culture results and will gladly share when we receive them.
villagelife: looking back I see that you were in on the earlier discussion. Great idea, though, seeking info on the other combinations (XMRV- with POTS, XMRV- w/out POTS, etc.). A little caution is warranted, though, in that the consensus seems to be that there is a substantial risk of false negatives with currently available XMRV tests, making interpretation (particularly with small sample sizes) of the answers collected for the XMRV- cases problematic.