The antenna gain should be mostly irrelevant as what is limited (by regulation) is the output (radio) power (EIRP).
This depends on the channel, it can be (ETSI) 20dBm (100mw) up to 30dBm (1000mw), but devices with fixed (internal) antennas such as those you mention) won't allow you to change the antenna gain and the sum of the fixed antenna gain + transmit power = allowed max power will be fixed limiting automatically the transmit power to not exceed regulations.
In theory, it should be better to have relatively low antenna gain as it means a fatter toroid (for omnidirectional antennas), see this picture:
and the actual speed depends on both the AP and the device that connects to it, and a very high antenna gain might be counterproductive, as it will also get more interferences.
The Wap Ax antennas are more directional, so they are not directly comparable.