Kestrel, I have flown models with all three of the engines you mention.

Powerwise, the ascending order is Magnum XLS, TT .46 Pro and, by quite a margin, the Magnum .52 XLS.

The .52 is definitely the strongest, seemingly by even more than its extra capacity would suggest. With an APC 11 x 6 as a test prop, the Magnum .46 will do mid elevens, the TT .46 Pro will do about 12K and the Magnum .52 will do around 13K.

Magnums can differ from engine to engine. Some can be sweet and others can be a little less than happy in their carburation. The .52 is a real hotrod, but will ultimately frag its stock rear bearing under hard use conditions and has been known to snap its crank between the bearings where the inlet port is machined. With new high quality replacement bearings, the .52 can be pretty reliable.

The Thunder Tiger .46 Pro is a real sweetheart and, although it's not as powerful as the .52 in static tests, it will unload really well in a pattern ship with a prop like the APC 11 x 6. Its bearings are durable and, at our field at least, the TT .46 Pro has proven to be among the most reliable and consistent of engines.

If you can sell the "CEO" a 10% overrun on your budget, consider the excellent AX .46 as well.

Edited to add: The .52 is essentially the same size and weight as the .46s. There's no penalty there.