At the bottum of this page : All about antennas
At the left side you can find the eznec plots of the Maco 3 and Maco 4 elements yagi.
There is about 1 dB gain difference between them, and the front to back of the 3 el is better.
However the front to rear of the 4el wins again.
I have written down on this forum dimensions for the 3 (or) 4 el to improve things. 4 element yagi specs
That will also get better performance compared to the signal engineering one.
The remark "not to bother with less than a 4el" is one i disagree with.
For DXing horizontal beam antennas provide additional groundgain.
This is much more than a vertical will provide.
For DXing a high placed beam (also the smallest one like a moxon) will beat the vertical and be a major improvement.
That high placed posistion will probarbly also mean the take off angle is much lower, hence less "hops". (Unless you have your vertical placed over a salt sea for example.)