I wonder if the OP is still with us?

I'm a fan of realistic tanks, but some of the combinations have proven problematic. I like the metal Tiger turrets, but I've gone back to plastic because the metal is just too heavy for that plastic upper hull, even with bracing (IMO). It's been my limited experience that for realistic performance, it's the unsprung weight that makes the biggest difference. Add metal roadwheels to any tank, even one as small as the aforementioned PzIV, and you'll see a remarkable difference.