The helicopter physics model is definitely simplified. It doesn't model torque, vortex ring states, asymmetric lift, rotor RPM and a whole heap of other factors which make choppers so difficult to fly in RL.
Having said that, in my (RL fixed-wing but not rotary-wing pilot) opinion the ArmA Apache is probably pretty indicative of the actual aircraft.
Going with data from Jane's All the World's Aircraft, the AH-64D has a maximum level speed of 143kts/265kph and g-force limitations of +3.5/-0.5 (compare that with +7.5g for an F-35B and +9g for an F-35A/C).
If you're doing 150kts then you're travelling pretty close to its max speed. Think about going flat out in your car: You're not going to make it round a narrow right-angle corner at that speed, are you?
Also a fully-loaded Apache weighs in at close to 10,000kg. It's a big vehicle and it's not exactly going to carve up the skies or pull a u-turn on a dime.
In RL Apaches aren't about going fast, they're about going LOW (typically flying below 30ft in combat), and they're built accordingly.
Flying it in ArmA, I find the Apache is most manoeuvrable at low-medium speeds. It also makes a difference how much collective (throttle in this context) you've got on: If you throttle back to zero you're basically gliding on momentum, so it becomes less responsive.
Cheers,
-=[CW]=-