As I'm sure you know (despite Matt Wald's stead-fast refusal to acknowledge it) United has an alliance with Delta, so once you get the miles in Delta you can use them for free *domestic* tickets on UA. I realize domestic may not be your thing, but that conversion rate just sucks by the time you get the miles to UAL.

BTW, the AMEX to DL to HHonors thing should take about a month total from what I'm told (a few days to go AMEX to DL, about a week to get your HHonors certificates from DL, then you mail them to Hilton.)