A couple of things working to our benefit.
-The 50% bonus, of course,
-With every 20,000 SPG points converted to 20,000 DM Miles, you get a 5,000 miles.
-Buy SPG points is 20% off until May 31, 2010. So right now, the max of 20,000 SPG points can be purchased for $560 instead of the regular $700.
So...
$560 can get you 20K SPG points, transferred to US Airways gets you 25,000 US miles + 50% of 12,500- so 37,500 miles. (must do so before 5/31 to get the 20% discount on SPG purchase points)
-Kinglobjaw