I rarely get challenged to duels by people with common sense anyways.
However, with the new patch and Modding Tools (which not everyone has to know about) you can drive a stage 3 Ferrari F40 and an AWD Saleen S7 which IMO fall into the same category as physics-modded cars.
Thing is, when we find a problem we tend to stop right at it instead of finding an ingenious workaround, which leads to banning everything. That's not healthy because with limited possibilities you'll invariably reduce interest in the game. For example, in GRID up to patch 1.2 you were allowed to use eBay cars online and those cars had an advantage over the regular ones. People found a way to edit the game files so that they could have super eBay cars. As a result Codemasters banned eBay cars from online play, without considering the fact they were the ones who included the eBay cars as an original feature of the game in the first place, a feature that rewarded the players who looked for them. And, despite the banning of eBay cars, people can still cheat with trainers and memory editors.
The main problem with banning physics editing is that people have already found a way to do it and it will be available to anyone who search for it. In the end, it penalises fair players who aren't aware of and/or don't know where to find these underground mods. However, I acknowledge that competitive online play may be at a serious risk if everyone has a different database file. This doesn't mean we have to reach a full stop on this matter!!! IMO it would be better if we could reach a middleterm. How we could do it is, however, a different discussion.