You might be adjusting the wrong setting. If the engine is "bogging down" on take-off, you might need to lean the low-speed needle a bit, rather than simply adjusting the high speed needle. A half a dozen tanks of fuel may have broken in your Magnum XLS .46 enough that the idle can be leaned out a bit; what was working when the engine was brand new is now a bit too rich.
I found the Magnum .46 XLS to perform well with a 10x6, 10x7, 11x5, or 11x6 prop. They don't require a lot of nitro, and will run as well on 5% or 10% nitro as they do on 15% nitro. They are fairly high compression motors, so you will likely get better results with a medium-hot plug like the O.S. 8 or Fox R/C Long plug rather than a hotter plug like the O.S. A3 or O.S. 6 (same plug, different model number). If you run an 11x7 APC prop (too much load) with an O.S. A3/6 plug (too hot) and 15% nitro fuel, you'll never get it to run reliably.
I also found that my Magnum .46 XLS tended to "unload" more in the air than some of my other two-strokes. When adjusting the high speed needle, I found my engine ran better if I turned it back a full 1/3 of a turn rich-of-peak rather than just a few clicks. Your mileage may vary.