I've been doing some tests with mediums and softs.
Results:
1 stint of 8 laps on softs
Best lap: 3.27.0
Total: 28.07.X
Note: conservative driving. Did some mistakes, estimated loss ~10 secs.
1 stint of 8 laps on mediums
Best lap: 3.28.7
Total: irrelevant
Note: agressive driving. Tyres were worn out after 7 laps. Took me 6 minutes to do the last lap.
2 stints of 4 laps on softs
Best lap: 3.25.6
Total: 28.18.X
Note: agressive driving. Made some mistakes here too, time loss should be around 6-7 secs.
Medium tires simply can't match softs performance wise, and don't last much longer. If I went for a smooth stint, maybe I could make them last 9 laps.
Softs deliver very good grip for the 5 first laps and remain decent until end of 7th lap. I was able to run a 3.29.0 on my 7th lap, only 2 secs slower than best lap. The 8th lap is a bit tricky, significant time loss should be expected (3.35.X).