Why avoid the 747? I prefer them, particularly when seated upstairs.
UA now has lie-flat seats on all of its 747 aircraft. Only a few of the UA 777 aircraft have been converted. There are also more seats to potentially upgrade into on the 747. than the UA 777 aircraft. If you're going on UA you really do want the 747. UA also offers service ORD-HKG, which cuts out the NRT connection and potentially late arrival time into HKG.
Regarding the upgrade itself, I don't know the details of the UA upgrade for miles scheme. I've always used SWUs.
h -- and I meant NRT-IAH in my post above...