I was away on a btrip for a week, if you want me to comment your gonna have to provide sources. It is impossible for HSPA+ to be more spectrum efficient the LTE, Googling around for news on tmo news all I found is this which seems to back my point:
Verizon Says They Use Spectrum Twice As Efficiently As T-Mobile
On the other topic, in 2013 all carriers are going LTE-Advanced from the looks of it.