I wonder what's the reason of picking groups of 5 elements instead of 2 or 8.
You still can do 3 or 4 but with slight modifications
https://arxiv.org/abs/1409.3600
For example, for 4 elements, it's advised to take lower median for the first half and upper median for the second half. Then the complexity will be linear
2. One and three are probably too small