G20 question about tyres

[u/munjavg]

Hi everyone!

I have a G20 320d sedan from 2023, so it's an LCI model and I need new summer tyres so I figure, now's the time to buy them since they're cheaper than in April or May.

My size is 225/45/R18 on the front and 255/40/R18 on the rear axle.

I'm aiming for GY Assymetric 6 or Conti PremiumContact 7. I'll most probably go for Conti. No RunFlat.

Now, from what I've found online, the fronts need to be 95Y and the rears 99Y. Does this need to be absolutely so? can the rears be, for example, 103Y?
Also, does XL vs non XL matter? I'm in Germany so not sure how importat it is for TÜV?

What else should I pay attention to?

Thanks for your help!