So the imminent version 1.3 (and Dream Pack 2) brings a whole new bunch of improvements, features and novelties.
Here's some previews regarding the driving (I wanted to write "warnings" but it sounded a bit too harsh :p )

64bit - 32bit.
Nothing changes in terms of driving and physics between the two. 64bits though permits addressing bigger chunks of memory and can do stuff like saving bigger replays. I do not know if this is already enabled by Stefano, but if not, will be in the future. Certainly 64bit is the way forward, so start updating too...

Physics:
- New ABS system which now supports 1,2,3,4 channels. Cars should stop better now. (obviously realistic distances)
- Active differentials also at the rear wheel drive cars. I'm not talking EDLs supporting mecchanical diffs but actual active differentials. They can do some great tricks... try the M4, Ferrari 458, Ferrari LaFerrari for some amazing results.
- EDL differentials now active also at the front of AWD active systems. Yes we managed to eliminate some (not all) understeer from the Por... sorry RUF AWD. The Nissan GT-R pulls some amazing tricks too.
- Modified Front splitter height sensitivity for some cars will make some famous turns not so easy to do.
- Added wheel offset simulation in suspension so that you can simulate more easily and accurately the correct suspension scrub. Scrub value is also available in the dev app "suspensions"

V5 Tyre model:
Our tyre model evolves with each release and this is a big step forward! We now have completely reworked load sensitivity equations, new over the peak curve, different flat-spotting based also on load, modified and corrected rolling resistance equations, new heating values and simulation of both surface and core temperatures with speed (from air speed) sensible cool down and more. All of that in the core system

Because of all those changes in the core system, we have put a massive effort to completely rework all the tyres for all the cars. That's more than 130 files each of one with at least 2 compounds, usually 3, sometimes 5... the struggle was (is) real.

As such, the bad news is that some of the cars are still on the V4 tyre model (which is still compatible so your mods also are not broken). The good news is that there are just 7 cars that are still on the V4 model, namely:
Ferrari 312T, Lamborghini Miura SV, Lotus 49, Lotus 98T, Lotus EXOS 125 (and S1), Shelby Cobra 427.
As you can see, they are all either extreme single seaters or vintage tyres. We need some studying to do for them and couldn't make it in time. Expect an update soon™

All the other cars are on the brand new V5 tyre model!

What to expect in terms of driving?
Nothing and everything.
As usual we have a pretty decent idea on what a tyre should do and that hasn't changed, so we don't believe you'll feel something completely new. More of a global improvement of weak points of the old model. Nevertheless my advice is: Forget everything. Forget your laptimes, forget your setups, forget your FFB settings, actually set everything to 100% gain as we changed how the FFB handles for all cars too.
Just drive, from scratch, without any muscle memory.

A few notes.
- Heat your tyres slowly. It will need 1 to 2 laps to bring the tyres to proper temperature both surface and internally in the core. The surface will keep going up and down but the core will stabilise. Then start to push. Otherwise use the tyre blankets
- What was the core temperature on the apps is now surface. Don't go crazy on the surface temperature. It is VERY variable now. It will go up and down in terms of mere seconds! What you need is a proper temp range on turn in, apex, exit. Ignore what it does at high speed on the straights, that's how it works. (look at some F1 heat cameras videos on youtube to understand the effect).
- Cars are even more sensitive to setup now. One click at a time.
- Did you spun out? It happens. But be VERY careful when you rejoin. It really takes nothing to overheat the tyres while doing burnouts to get back on track. The next turn might be fatal! Take it easy for at least 2-3 turns to cool the tyres down.

And a mea culpa. The new heat tyre model is extremely complicated. We should have made a proper app or proper messages to warn you when the tyres are cold, overheated, good or bad condition. We didn't make it. We apologize, we will try to do it... err... soon™. Please be kind and have patience, it's complicated for us too and days have only 32 hours.