The stutter and fps drop you are seeing with the HD4600 is a known issue in complex games or ones that use a lot of effects and in particular, WebGL shaders. Intel's OpenGL performance is attrocious and their drivers for it even worse. They seem to only care about DX and not OpenGL for gaming.
I posted something regarding CPU usage here:
Essentially, C2 is single threaded for the most part, all that logic uses 1 out of 8 threads on your i7 CPU. It can max out on 1 thread, when it shows 99% CPU use, the game will bog down and frames will be dropped, regardless of your GPU.
So be very careful when you design a bigger complex game, ensure that the reported CPU use stay less than 50% on your i7 as its a very strong CPU with high single thread performance. Someone on an older CPU, or an AMD CPU with weaker single thread performance, will suffer greatly if you are designing your game to go beyond 50% of an i7's single thread capability.
Also if you want gamers to play it on Intel HD graphics, don't use WebGL shaders. Maybe do a "Low/High FX" option, low for people on Intel iGPU and High for AMD/NV GPUs.