durability vs repair time
I didn't take a screen shot, so the repair times may be slightly off. (I was basing original time off difference from t5's original time) But a T3 Light tank definitely repairs faster than a T4 medium tank of same durability (almost 7 minutes faster, for 1158LT vs 1194MT)

Light tank- Durability/45 Medium/heavy tank- Durability/38, Destroyer- Durability/40 (no artillery died on this run..)

Dura {minutes} dura/min tank
2078 {55} 37.8 t3h
1158 {25} 46.3 t3l
946 {27} 35.0 t3m
570 {14} 40.7 t4d
1194 {32} 37.3 t4m
2720 {71} 38.3 t5m