Barely noticeable. The GPU isn't much of a performer in these Core M chips, so don't expect much out of it.
But does the GPU clock speed go up proportionally to the CPU clock speed?
These Intel processors have more configuration options than before. They don't use a fixed spec, so we could find all 3 macs use the same processor model but with minor changes to CPU clock. As they're so customisable, it's not possible to say whether the GPU will be faster.
The below link shows the Core M range.
http://ark.intel.com/products/series/83614/Intel-Core-M-5Y-Mobile-Processor-Series
The HD5300 it's almost equal to the 2012 HD4000
Synthetic benchmark averages put the HD 4000 well above the HD 5300 - well, that's relative, they're both low-end GPUs (the type of low end where slow and slower are hard to tell apart).
Can you provide a source for that, please?