After I tried both games switching more frequently between them, I have a clearer view about the physics discuss.
- Physics: SLRE is noticeable better. The cars have more feeling of wheight. In Dirt Rally is easier to change direction, the cars feel noticeable lighter (in RBR they feel even lighter). Compared to a benchmark like Assetto, definetly SLRE is is the closest of the two in terms of weight shifting.
This is also perceptible when using handbrake. In SLRE it feels like it should be in reality: the rear tyres block and the rear of the car slips through the surface. In Dirt there is a sensation like the rear is being pushed in the direction you want; like there is a guy outside the car pushing with its hands the side of the car to rotate it.
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Tyre model: this is a different discussion. Tyre model on ice is a very clear win for Dirt; the car feels much more slippery and very close to what I see on television: you see the real cars trying to perform the straightest line possible; like in Dirt Rally. SLRE feels much more forgiving in this surface, feeling like it was snow with a little bit less grip.
On tarmac there is no discussion. Dirt Rally is objectively
trash, one of the worst results on tarmac I've ever seen (a youtuber that recently tried Dirt 4 said Dirt 3 felt even better than Dirt Rally). SLRE is very good indeed, compared with PCars, feels closer to AC: you have to drive more finely, the driving line is clearer. In PCars you feel more that sensation that you throw the car into the corners instead of driving through them.
In the rest of the surfaces, I believe they are more or less on par. I can't right now find noticeable differences between them. Both feel great for sure.
- Force Feedback: tarmac doesn't need discussion, does it...?. In the slippery surfaces thought, I feel what
@bogani said. The wheel sometimes do opposite force (when turning the steering at high angles). In doesn't feel completely unnatural (on tarmac does), but in SLRE there is no such effect never. Is it realistic to have it or not to have it? I don't know, but it certainly feels a bit weird.
Maybe that is related with this: when oversteering on slippery surfaces, SLRE feels just as good as Dirt with RWD cars (although IMO dirt rally has a more realistic rear tyres grip) and much better with FWD cars (some of the pro 2WD class cars on SLRE remind me a lot to the 500 abarth on Assetto Corsa).
There are another details about force feedback: in Dirt Rally you feel better and faster the disconnection of the tyres with the road when jumping, the irregularities feel better on Dirt rally...
Conclusion: overall, SLRE has a noticeable better feeling in general.
edits: typos