what is the impact of smaller bit size sbox
the differential property , linear property , algebraic order is larger for 8 bit s-boxes compared to 4 bit s-boxes. 

The optimal differential/linear  probability is 2^-6 for 8-bit s-box while it is 2^-2 for 4-bit s-boxes, therefore less number of active s-boxes needed (less rounds) to achieve minimum differential/linear security bound using 8-bit s-boxes.

However, 4-bit s-boxes are good for light implementation and threshold masking to resist side channel analysis.