Well judging by the sudden falloff of X51 wireless issues since Jan 1, 2013, it would appear that all the wireless issues with the X51 have been solved. Had Dell Support to the house 3x first to replace antenna and DW1502 wifi mini board, second time again to replace DW1502 and the third to replace the DW1502 with the DW1506. All three attempts failed within 2 to 24 hours with wifi conntection either falling off or not at all. BTW - on the last contact with Dell Support I requested replacement of the Atheros DW1506 Mini Card with an Intel 5100. I was denied that request and told that Dell would only replace the DW1502 with the DW1506 which they are still providing in the X51 PC's.
Well at the point when the DW1506 failed (4 hrs) and after reading in reivews on the web what garbage Atheros makes (at least in wifi cards) I purchased a Dual Band Intel WIFI Link 5100 Half-Mini PCI-E Card H006K purchased on eBay for $7.36 including free shipping. Needless to say - PROBLEM SOLVED!!!! My download and upload speeds are steady at the same speed as the Ehternet Cable I used while waiting for the new card to arrive.
So in the event any of you are still getting the Antenna and Atheros Card runaround from Dell Support, here is the ebay link to your problems solution:
http://www.ebay.com/itm/121033112028?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649
Another satisfied Dell Support Customer.