Thank you for you input on this.
The indoor APs do not support (are not certified) with outdoor antennas. The list of antennas that are supported with each AP is included in the datasheet. For the 3825e, the WS-AI-DX07025 would be the comparable antenna from an RF footprint perspective.
You are not allowed to exceed the EIRP in your region so even if the antenna has more gain you must reduce the tx power so you are not over the EIRP value.
The other thing is that the antenna has N-type connectors so even if you would use it you would need 6xpigtail from N to the connector on the AP3825e.
I assume that would be on the pricy site and you'll add more attenuation on the link => longer cable, another connection,
I think the 25degree sector should be fine for the 30 feet long hallway.
Hope this helps!