Do Construct 2 games generally perform a lot better with Node-webkit than on a web browser?
I own all the engines from Game Maker through to C2 and each has its strengths and weaknesses. I would rate Game Maker closest to Construct 2. But that is my preferences. Of course Unity3d is awesome, but has a extremely steep learning curve.
Node Webkit (Node = node.js | Webkit = Chrome) so it actually is running via a web browser so performance is excellent.
You can bring a small game to a standstill if you don't program properly. You can run a big game on mobile, it all depends on you, your skill level, etc etc etc.
A 5 year old PC leaves lots of room to design, even carelessly, and graphics no matter what engine is what will cause you issues. Thisis all you need to really watch out for