Not a huge performance impact, but measurable. Check reviews out to check the performance difference between the two GPUs.
Usually the metric I look at most is the number of shader cores because at the end of the day images in games are massively parallel which favors swarms of processors.
The modularized approach seem as much a design constraint as anything given how complex an ALU can be when cloning a Cray Y-MP etc. NVIDIA has changed their core modules so much that it makes it hard to figure out.
I see some more recent GPU products with a lot more GCN modules but I play at 1920x1080 so how many do I really need? Even Ashes of the Singularity is very playable.
My chess site has a Cray as the mascot, and I have played chess on a Cray which does play a lot better than a PC does with its better CPU. I have a pic of the Y-MP with some comments comparing it to a modern microcomputer.