Multi core games most of the time load 80% of the work on one core, one thread and only some cosmetics on other cores.
This is due to the fact that it is quite hard to multi thread applications like games to all the different cpus out there.
I think only 2-4 games nowdays use good multi threading, Starcraft 2 being one of them, other games might be physx heavy games.
Why you think we have been getting dual and quads from both AMD and Intel since the Q6600 in 2007? 😀.
And many games will still run fine with 2 cores (by fine I mean the limiting factor to good frame rates will be the gpu, not the cpu).
I used a i5-2430M (dual core, laptop) untill I upgraded. It is about the same performance as a G860 (lowe end dual core desktop).
And the limiting factor was still the GPU in almost all games I played.
What you wont be able to do is play and stream with dual cores. That requires more cores to split the workload.