Its a little like comparing 2 different types of apple to fair, they are both apples, but of different taste.
They are both well made, fillet brazed, craftsman born. but hard to compare, because of geometry and tubing types, the closest comparison would be the Columbus Max Pioneer, to the white spider, the majority of pioneers you will see have a lower grade of tubing and have a Lugged BB shell. Even then you have to factor in they would both need to be the same model year, and handbuilt for riders of a similar build to draw an objective comparison to be fair.
Suffice to say, the mainstream pioneer was built to hit a price point and compete at a level with Orange Clockworks et al, the Roberts White Spider was another level again, the custom built choice for those who could afford it, and the ride of choice for pro racers like Gould and Baker for the world circuit dressed in Peugeot team colours.
both are exceptional handbuilt steel fillet brazed Uk designed and fabricated, popular, sought after, and becoming hard to find, both have there fanbase and rightly so....
