Solid bearings have less drag than roller bearings at speed. The initial start up from a dead stop might favor roller bearings but the  mechanical drag of metal against metal in a roller bearing causes more resistance at higher speeds,

Roller bearing are superior when it comes to minimal amounts of lubrication where as a solid bearing will quickly fail under the same conditions.

Internal combustion engines are a prefect example of this. In 70's and 80's a lot of motorcycle engines were built using roller bearings on the crankshafts and connecting rods, As the power in these engines continued to elevate to higher levels these engines went to solid bearings for cranks and rods because of mechanical drag and horsepower loss.

A  somewhat educated guess, but a 1000cc 4 cylinder engine at 10,000 rpms will probably make about 10 hp over a similar engine with roller bearings. 

Two cycle engines, with roller bearing cranks and rods with a slight amount of oil mixed in with the gas will live a long time. They could make more power if they used a closed loop pressurized oiling system but that presents another set of problems not for discussion on a  freight car related message board.