I frequently flying to Singapore from Florida, and have transited through IAH, EWR and IAD, and have been able to come up with itineraries with around 2-hour of transit time at SFO for the evening departure of SFO-SIN flight.
I have found using miles to Singapore to be a waste due to the high redemption rate. If flexible with dates, fares are quite competitive since there are competions for direct and indirect itineraries.