The decision is not a result of an attempt at a back-to-back data gathering exercise, but is simply down to the preferences of the individual drivers.
The team took a different direction with the upgrade package, first seen at the United States GP last month, and has since earned some solid midfield grid positions.
However, the cars are still proving hard in their tyres over a race stint, leaving the helpless drivers to drop down the order.
“The main drive behind this was Nico feels that for him the old spec suits him better, and Kevin is the opposite,” said team boss Guenther Steiner of the decision to run both versions.
“We’ve opted to give them what they want, we have two races to go and nothing to lose, so we’ve tried to do what we can.
“We could discuss gathering data, but we’ve got enough data, it’s a decision based on what each driver likes more than anything else. It puts them in a comfortable position so that they’re as happy as they can be with the car they get.”
Source: Autosport