It isn't the fast angle wheels that actually improve the rolling characteristics, it is the switch from having the wheels rotate on the axle to having the axles rotate with needlepoint ends. The angled wheels facilitate the design by shifting on the rails while going around curves.
I have a source for this: page 101, first full paragraph on the right hand column, "Lionel, A Collector's Guide and History, Volume IV: 1970-1980"