FM4's Sounds = Over-exaggarated to even sound like the real cars, if I'm honest.
Damage model = Well, if you like more Pre-made impact points than actual real time based, then it's only about a choice, oh and FM4 doesnt have windscreen modelled at all from the cockpit and is invincible and it doesnt have chassis damage.
Car Selection = This is true, but ONLY if you bought the DLC, without those, the list is almost identical with FM3 (without the Porsche)
Career = FM4 is identical with the FM3's career, almost, they took away the endurance races due to the lack of fuel consumption which is made all wrong in FM series.
Graphics = Only blind person can really say FM4 looks better than GT5, cant fool anyone who actually has both.
AI = in FM4 it is certain that AI will ram onto the player car whenever player is braking at the corner, these dont care are you there or not.
Better DLC = Depends, FM4 has received any new track at all, and only DLC cars are really interesting but there is some cars I personally dont understand at all, Jackson's Charger for example.
T10 ahead of PD = IF T10 can ever create tracks, surfaces or cars right then it could happen, but I doubt that will happen before FM X appears.
Sam, owner of the both games.