The only difference between the XP-9-20 and XAP-9-20 is the angle on the bottom of the transducer.
Whether the XAP will work better or not on an angled hull would depend on the angle of the hull. The XAP-9-20 was meant for hulls that have a deadrise angle of 14 degrees or more.
The temperature sensor in the XP-9-20-T will not override anything. If you have this and the XNT-9-Si-180-T transducer both connected to an AS-Si-DB-Y cable than the temperature will always come from the XNT-9-Si-180-T transducer as there is no electrical connection made to the temperate sensor in the XP-9-20-T transducer when using this cable.
If you connect the XP-9-20-T transducer and the XNT-9-Si-180-T transducer to a TS2-W Transducer Switch; than whichever transducer you have the switch set to will determine which temperature sensor the unit will use.