There’s a good reason why the power peak sits on the redline - the cheap hypereutectic cast pistons can’t take any more than that! You should have gone with forged pistons, tuned the engine for 95 RON, and extended the redline by a reasonable amount (but not to the point that the pistons become overstressed) to fully unlock the engine’s potential.
And to combat unwanted oversteer, remember this tip I gave when I hosted CSR 137:
Also note that the suggestion to increase or decrease front or rear tire width (due to it being either too wide or narrow for their load) is just that - a suggestion - and does not need to be followed all the time (it shows up as a blue marker in the list of warnings). However, oversteer warnings (which show up as yellow) definitely should be fixed in order to make your design workable.
And regarding brake fade: Although it can be caused by undersized brake rotors or the use of less advanced types, as well as overly comfort-biased pads, more often it’s a result of using too little brake cooling. For high-performance cars in particular, it’s not a good idea to deprive the brakes of cooling airflow. Last but not least, a quick look at the suspension tab also reveals that you used standard springs, not progressive-rate springs - most cars use the latter because they confer a gain in drivability, comfort and load capacity that more than outweighs the loss in sportiness compared to standard springs.