Frame rates are irrelevant. The Intel video chip simply does not have the hardware processing to do many things 3D graphic related. It lacks features and is easily overwhelmed. It has a small internal cache buffer.
You need to set the "Maximum Texture Size" to 256. You should not be running with "Detailed Terrain" enabled in the "Options->Graphic Details->Advanced" panel either.
Just try it and it should stabilize things.
So I have this same problem, and I have tried everything you have said above, but its still not fixed. I lowered the max texture to 128, turned off detailed terrain.
My system:
Operating System: Windows 7 Home Premium 64-bit (6.1, Build 7601)
Processor: Intel(R) Core(TM) i7-2630QM CPU @ 2.20GHz (8 CPUs), ~2.2GHz
Video Card: Intel(R) HD Graphics Family (Radeon HD 7470m)
Memory: 8192MB RAM