Darstaed Roller Bearing comparison

Quite often the brake blocks on the Darsraed bogies rub on the scale 3'7" wheels. But even when they've been filed clear or replaced the running still isn't 100% free-rolling. Because I want to haul 8-10 of them up gradients of around 1 in 70ish and I run battery power I need them to be as free running as possible.
The second BG has been fitted with roller bearings and Peartree wheels. Outstanding!