The 390 is competitive with the 970 at stock settings, but the 970 can see as much as 40% fps increases overclocked..... whereas the 390 sees increases of up to 8%. The 380 isn't in the running.
If there is no affect on gaming?, why was there such an 'uproar' over it not having 4GB?
It did have 4GB of vram. People don't like it when information is being left out - that there is 3.5GB of faster vram +0.5GB vram of slower.
Performance of the GTX 970 remained the same with or without the knowledge of this.