Thanks for the advice guys! 
I just finished the race. Placed 2nd, no mistakes + new pb, so all in all a very good race for me. 
And I think I learnt something: before the race I considered either doing as Bob said and move more power to the rear tyres, but I tried it a few laps and thought it altered the handling of the car too much. So instead I used the R4s on the front tires. I kept an eye on the tire temps, and they were fine, until around 15-25 laps or so when the temp really dropped. I know it's supposed to, and now I experienced it first hand too.
So in retrospect I think I should have used R3 instead of R4 on my front tires, but R2 worked fine on the rear ones.
Here's the graph from the manual:
So: all in all a great day -- I learnt stuff about setups, and I had a good racing experience.
I just finished the race. Placed 2nd, no mistakes + new pb, so all in all a very good race for me. And I think I learnt something: before the race I considered either doing as Bob said and move more power to the rear tyres, but I tried it a few laps and thought it altered the handling of the car too much. So instead I used the R4s on the front tires. I kept an eye on the tire temps, and they were fine, until around 15-25 laps or so when the temp really dropped. I know it's supposed to, and now I experienced it first hand too.
So in retrospect I think I should have used R3 instead of R4 on my front tires, but R2 worked fine on the rear ones.Here's the graph from the manual:
So: all in all a great day -- I learnt stuff about setups, and I had a good racing experience.