I recommend you to check your GPU usages. A few users have reported that the Nest app can use up to 45 % of GPU power when the simulator isn't even running. Some performance problems aside, I have to say that I really like this plane, even though I've kind of slept on 757 until recently. Time will tell if it's worth the price.
I'm a bit confused about the roll rate. The SWS PC-12 rolls quite slowly and this version feels like a fighter jet in comparison. Perhaps the NGX behaves like that in real life, but I haven't seen anything that would suggest that's the case. I haven't read anyone ever complain about this, so maybe it's just me.