A .46 will balance because we mount all the radio forward to balance the .25 and .15. You could move the battery and servos rearward to accommodate the heaver engine.
The only thing I would caution you about is that because our kits use a semi flex design for durability, there is a limit to the air speed. Because of the flexible design if too much speed is reached the wing may flutter. With the longer the span of the panther this may be more noticeable than in the Predator.
I would start with an 11 X 5, and use plenty of 3M77. Good luck