It is quite astonishing that not one single person who has been asked to provide evidence to back up their claims over the past couple of months has been able to do so.
You can't really blame him, nor majority of people who drags themselves into such discussions without proper idea of the backgrounds of claims of the people on the opposite side.
It is quite hard to make a *proof* out of anything related to the actual physics and such through videos and words on screen. Sensation of physics is very subjective and personal *idea* which really needs to be felt and experienced properly in order to comprehend the subject.
Through past years I was one of the greatest critics of the Forza physics. First Forza is still a joke in my book, no discussion there. However, Forza 2 was a generational leap compared to first game, especially in two areas: collision physics and sensation of non-ABS braking. However, at the time, Forza 2 didn't support any serious FF wheel and all superiority of the those two areas were overshadowed by 270 degree steering-limit and poor implementation of FF support for MS and LTFX wheels.
When Forza 3 arrived, with proper 900-degree support and new physics, it seemed great on paper. But they've introduced the infamous stability/linearity assist, while both collisions and non-ABS braking sensation were drastically toned-down compared to FM2 probably in order to make the game more accessible. Also, the suspension-modelling was pretty much non-existent from perspective of active geometry, it was dull, non-responsive and sensation of the overall handling was not exactly convincing.
But Forza 4 changed everything. After the first (and only) patch that effectively took care of infamous stability/linearity assists and with introduction of the fully-released Simulation physics-mode - where tire-thread, tire-grip and tire-threshold are absolutely the most important substances - physics of Forza 4 has reached a new levels, absolutely comparable with GT5.
Also, with the work done with Fanatec company and introduction of the two new wheels with special firmwares that can utilise the full scope of the new wheel-support engine (CSR and CSRE models), Forza 4 became a different game than any other FM games before.
On some other forums I was even called a troll because of my criticism regarding previous states of physics in the FM series. However, after the great experience I have with FM4 in last 3 moths I can safely say that there are only two types of persons that can criticise FM4's physics in any *console-simulation* related debate and insist it is still inferior to GT5's: either intentionally malevolent or totally misinformed.
Either of those can't be perceived as a serious collocutor in this particular discussion.