That's interesting because I feel the exact opposite - Greyhound on Cobra for me usually means death from miles away, while on Luttich I can zip in and out of cover. I still run into Panthers irritatingly more often than I should on Luttich, but jeeps, APCs and the Puma you can take out one-shot head-on, and the tanks apart from the Panther are easy kills, provided you see them first.
The StuG is a bit tricky because of the small part of the rear you can damage it, but you can just drive circles around it until you finish it off. The Panzer IV is a bit harder, because although you need less shots to kill it (often one, and never more than two, to the rear), it has a turret. My strategy is to approach it on an angle and fire the first shot, and then if you don't get a kill, if he starts the turret turning right you gun it and drive straight ahead until you can get the second shot, and if he turns the turret left, you reverse for the same result.